In Chad, hepatitis B virus (HBV) is thought to have a high prevalence and is consequently responsible for numerous acute and long-term complications. It is often detected during screening in potential blood donors. However, no general population-based study on the prevalence of hepatitis B has been performed. The aim of this study was to gain an impression of the HBV prevalence in rural areas in south-west Chad. A total of 1309 individuals (745 boys/men, 564 girls/women) with a median age of 15 years (age range, 6–81 years) were screened for the presence of the hepatitis B antigen (HBsAG). We found an overall prevalence of 22.9%. The youngest age group (6–15 years) and the boys/men showed a significantly higher HBsAG prevalence compared to the older groups and the girls/women, respectively (P < 0.01). Vertical infection during birth and horizontal infection by sharing food, water and shelter are believed to be the main sources of infection.