Worldwide, around 780 million people lack access to improved drinking water sources and 2.5 billion lack improved sanitation (WHO, 2013c). The United Nations (UN) declared access to drinking water and sanitation a fundamental human right in July 2010 (UN, 2010). Each year there are approximately 1.7 billion cases of diarrhoea worldwide. It kills around 2.2 million people globally each year (4.0% of all death), of which 760,000 are children under five years old, mostly in developing countries. Diarrhoeal disease is the second leading cause of death in children under five years old (WHO, 2013c). The lack of drinking water, sanitation facilities and good hygiene practises are considered the main causes for diarrhoea (WHO, 2013d). For this dissertation, a specific health intervention (CBHFA - Community based Health and First Aid) was evaluated which had taken place during three years in 20 target communities in Bokeo Province in Lao PDR. The activities were in the field of water supply, sanitation facilities and hygiene education against diarrhoea. Objective: The objective of this survey study is to show that hygiene behaviour changes in a certain target population through the implementation of CBHFA, if a) individuals have access to improved drinking water sources; b) have access to a HH latrine and c) receive hygiene information. An improvement by 50.0% for each of the hygiene indicator: water use and treatment, hand washing, sanitation, food handling, waste disposal and cleanliness was considered a behavioural change and thus an illustration of the effectiveness of CBHFA. Methods: Hygiene behaviour was measured before and after the CBHFA intervention through above mentioned hygiene indicators. Quantitative figures were collected at two different points in time, in a pre- and post-survey, then analysed and evaluated. Interviews and observations were done through community assessment/evaluation with 20 focus groups in all target communities. 488/487 (pre-survey/post-survey) households (HHs) were interviewed and observed. Knowledge about diarrhoea (definition/signs, prevention, danger, treatment and modes of transmission) was tested. The change in hygiene behaviour as well as the water and sanitation situation was measured through a comparison of the pre- with the post-results. The Relative Risk (RR) and Odds Ratio (OR) were calculated for different variables, such as ethnicity, gender, education, age and income and their changes before and after the implementation of the health intervention project. Results: Water use and sanitation This research clearly shows that the availability of a public water system (gravity fed water system) in the target communities has increased (from 45.0% to 85.0%) as well as the availability and use of hand flush pit latrines (from 20.2% to 63.7%). 95.2% of HHs that owned a latrine used them. The water treatment through “boiling” (from 70.1% to 75.0%) in HHs has improved, but not significantly. Open defecation (OD) decreased from 78.9% to 34.7% (by 56.0%). However it is still practised by more than a third of HHs. OD is one of the highest transmission risks of diarrhoea and can only be eliminated by 100.0% sanitation within the community (WHO, 2008). Hand washing There has been a significant increase of interviewees washing their hands with water and soap (from 8.0% to 38.0%). This result was confirmed by observing the existence of soap in kitchens with 33.0% and in latrines with 20.3% of HHs. The ORs calculated for hand washing “with water and soap” and compared for each stratum of the variables gender, formal education and age group show no statistical difference, but there is a statistical difference regarding income and washing hands “with water and soap”. Relevant occasions for hand washing, such as “after defecation” and “before food preparing”, that could reduce the risk of the transmission of diarrhoeal diseases have not achieved a meaningful improvement. Waste disposal Waste disposal, such as collecting and burning has increased from 23.4% to 42.5% (by 81.6%) according to the HH responses. A matter of concern is the increased HHs (from 26.8% to 29.0%) that disposed their waste by “throwing the waste outside the village”. This waste disposal method is statistically different regarding formal education. The number of HHs with non-educated interviewees where this method was practised has increased over the intervention time in contrast to the number of HHs with educated interviewees. Knowledge about diarrhoea Knowledge was tested. The definition/signs of diarrhoea, its prevention, danger, treatment and modes of transmission were not known by more than 50.0% of the interviewees. It seems that hygiene indicators can improve without this awareness, if improved water and sanitation facilities are provided. However, further investigations are required. The results show that knowledge about diarrhoea is not statistically different regarding formal education and age, but regarding gender. Giving at least one right answer was higher in women than in men. Results and income The results of the pre-survey show that income is significantly associated with owning a latrine and using water vessels, such as pots and jars for drinking, but not associated with using soap for hand washing. However after the implementation of the health interventions, the comparison of the ORs of the HHs with low income per capita (≤200,000 LAK, exchange rate: 1 EUR=10,000 LAK) versus the HHs with high income per capita (>200,000 LAK) shows a statistical difference regarding hand washing “with water and soap”. The OR of the high income per capita group is stronger than the OR of the low income per capita group. Owning a latrine does not show a statistical difference regarding income due to the provision of subsidized latrines by the health intervention project. Occurrence of diarrhoeal diseases The pre-survey results clearly show that diarrhoeal diseases ranked at the top of all recorded cases of diseases. The post-survey results show fewer villages with diarrhoeal outbreak and reduced numbers of reported cases. Summary: An improvement by 50.0% has been reached in hand washing with water and soap, reduction of OD, safe food (by covering), waste disposal (by collecting and burning) and cleanliness but no improvement has been reached in the hygiene indicators “water use and treatment” and in crucial “occasions for hand washing (after defecation, before food preparing)”. Therefore the CBHFA intervention is considered only partially effective in the field of hygiene behaviour change.