Helicobacter pylori (H. pylori) infection causes achlorydria, depressed gastric acid barrier, impaired immune response and is suspected in bacterial overgrowth and diarrhoea. These features of the infection are known to cause significant malabsorption of nutrients and impairment of linear growth in children. The prevalence of H. pylori infection in children is known to be much higher in developing countries, especially among the lower socio-economic groups. The true prevalence of infection in urban children in Mexico and its impact on their growth are largely unknown. This study examined the prevalence of H. pylori infection in school children from an urban area in Northwest Mexico and attempted to identify the risk factors that predispose individuals to infection in childhood; as well as to relate the presence of this infection to growth of children. The cross-sectional study was conducted in 1997/98 in the poorest socio-economic sectors of the city of Hermosillo, Sonora, among 178 children aged 9 and 10 years. H. pylori status was determined in children by the 13C-urea breath test. Anthropometric (weight and height) and haemoglobin measurements along with analysis of faecal samples and a 24-hour dietary recall were carried out in each child. Family sociodemographic/socio-economic status and living conditions data were elicited from parents by interview via structured questionnaires. The overall prevalence rate of H. pylori infection for the children in Hermosillo as determined by this study was 47.1%. The findings indicate that rural-born father, number of siblings, the type of main water supply (one tap in the yard) and the sharing of bed by the study child are important risk factors for acquiring the H. pylori infection. A borderline significant but small effect of H. pylori infection on height for-age was observed in this study. H. pylori infection was found to be positively highly associated with Hymenolepis nana. No differences in mean energy, protein and iron intakes between H. pylori positive and negative children were observed. However, significant differences in the mean energy, protein and iron intakes were observed between boys and girls. H. pylori infection and enteric parasites were not significantly correlated with the presence of anaemia.