Child maltreatment is not a new issue. It has existed in various forms in every society since the early days in history. However, it is only in the past four decades that abuse and neglect of children has attracted widespread interest among health professionals and the general public. There is now a large body of evidence that identifies four main maltreatment forms: physical, sexual, emotional maltreatment and neglect. Child maltreatment is a substantial public health problem, as it is associated with immediate and long-term health problems. Most research into child maltreatment has been conducted in English-speaking, developed countries. Although there has been a small but steady increase in the number of studies from less developed countries over the past decade, there remains a relative dearth of research in these populations, especially in Asia. Over the years, most research projects around the world tend to be focused on only one type of child maltreatment (usually either child sexual abuse or child physical maltreatment), and many studies do not examine risk factors in depth, or address the possible outcomes of various forms of maltreatment. Children have always held a very important place in the culture and traditions in Vietnam. In 1989, Vietnam was the first Asian country and the second country in the world to sign and ratify the United Nations Convention on the Rights of the Child. Since then Vietnam has adopted various measures to promote children's rights and particularly children's rights to be protected from abuse and exploitation. Despite strong political support for the rights of children, there is little formal research into child maltreatment. From the small amount of available evidence and media reports, it appears that children in Vietnam are vulnerable to maltreatment, just as they are all over the world. It is clear that information about the extent and health consequences of different forms of child maltreatment from scientifically sound studies is still far from sufficient. Thus, more research is essential to ensure effective and culturally appropriate responses to protect children from maltreatment. The primary aim of this research was to examine the nature and co-occurrence of four forms of child maltreatment including sexual, physical, emotional maltreatment and neglect among Vietnamese secondary and high school adolescents in both urban and rural settings, and determine the extent to which such adverse experiences impact on self-reported health risk behaviours and physical and mental health. A mixed methods design including qualitative interviews and focus group discussions, and a cross-sectional survey was employed in this study. Incorporation of qualitative inquiry added a cultural dimension on child maltreatment and informed to develop appropriate quantitative measures. Following 8 focus group discussions and 16 in-depth interviews as well as a pilot study of 299 adolescents in Vietnamese schools, a cross-sectional survey of 2,591 adolescents randomly selected from eight secondary and high schools in one urban district and one rural district was undertaken between 2004 and 2005. Data were collected by self-administered questionnaires in class rooms. Key information included demographics, family characteristics and environment, and four scales measuring sexual abuse, emotional and physical maltreatment and neglect as well as standard brief assessments of health related risk behaviours, mental and general physical health. The study clearly revealed that experiences of different forms and co-occurrence of child maltreatment among school adolescents were prevalent in Vietnam. The prevalence estimates of at least one type of physical and emotional maltreatment, neglect and sexual abuse were 47.5%, 39.5%, 29.3% and 19.7% respectively. A significant proportion of respondents (41.6%) was exposed to more than one form of child maltreatment, of which 14.5% and 6.3% experienced three or four maltreatment forms. Results from multivariate logistic regression analyses showed that the prevalence of child physical and emotional maltreatment and neglect among adolescents was not statistically different between urban and rural districts. However, children from rural schools were more likely to report unwanted sexual experiences than their counterparts in urban schools. There was no significant gender difference in reports of adverse sexual experiences. In contrast, girls were more likely to report emotional maltreatment and neglect whereas boys were more likely to experience physical maltreatment. Furthermore, family environment assessed by parental quarrelling, fighting, perceived quality of parental relationship and emotional support appeared to be the most consistent factors significantly predicting each form of child maltreatment. After controlling for a wide range of potential confounding factors, many significant correlates between each type of maltreatment, each level of maltreatment co-occurrence and each health risk behaviour were found. In general, the pattern of correlations between child maltreatment and health risk behaviours was similar for females and males. Emotional maltreatment significantly correlated with most behaviours examined. Physical maltreatment seems more likely to be associated with involvement in physical fights and being threatened. Sexual abuse was significantly related to smoking, drinking, being drunk, and involvement in fighting. Statistically significant associations between neglect and self-harm such as involvement in fighting, feeling sad and hopeless, suicidal thoughts and attempts were found. Clearly, co-occurrence of child maltreatment was significantly associated with almost all examined health risk behaviours and a dose-response relationship was observed in most of the dependent variables. Regarding continuous measures of mental and physical health, multivariate regression analyses revealed that presence of four types of child maltreatment explained a small but significant proportion of variance (from 5% to 9%), controlling for a wide range of background variables. Additionally, while each form of child maltreatment had independent effects on depression, anxiety problems, low self-esteem and poor physical health emotional maltreatment appeared to be the strongest influence on mental and physical health of both female and male adolescents. Analysis of variance also clearly suggested that exposure to increasing numbers of maltreatment forms significantly increased the risk of mental and physical health problems in a dose-response fashion. The present study extends a small body of previous research examining poly-victimization in developed nations to an Asian country. The data contribute new knowledge on cross-cultural child maltreatment problems. Considerable commonalities as well as some differences in the findings in Vietnam compared with earlier research were found. One important conclusion concerns the significant independent associations between various types of child maltreatment, as well as the cumulative effects of poly-victimization on a wide range of health risk behaviours, depression, anxiety, self-esteem, and general physical health. This pioneering research in Vietnam provides timely and substantial evidence that can be used to raise public awareness of the nature of child maltreatment and the harmful effects of not only sexual and physical abuse but also other forms of emotional maltreatment and neglect which have not received attention before. These results from a community-based sample have demonstrated the urgent need for prevention programs. The current study provides an impetus for more comprehensive research in this sensitive area in the near future so that culturally and politically relevant evidence-based responses to child maltreatment can be developed in Vietnam.