So far little was known on the epidemiology of hepatitis A, B, C and of AIDS in Cambodia and especially not in the rural area of Takeo. Therefore serological markers for past or ongoing infections with the disease causing viruses were measured in 559 healthy individuals (305 adults, 200 children and 54 mothers of children with liver disorders) and in 185 individuals (103 adults and 82 children) with liver or kidney diseases. In none of the 744 samples tested was anti-HIV detected. 10-37% of the children and 73% of the adults showed HBV-markers, HBsAg being detectable in 2-14% of the children and in 8% of the adults. The prevalence for anti-HCV was 6.5% in the adults with a predilection in males (9%). No markers for HCV infections were found in children. Growing, age related proportions of children (27-97%) and 100% of the adults were anti-HAV IgG positive. HBsAg was detected in 46% of the adults with acute hepatitis, in 45% of those with chronic hepatitis/liver cirrhosis and in 90% of patients with hepato-cellular carcinoma (HCC). In children the corresponding figures were 18% for acute hepatitis and 18% for chronic hepatitis. Patients with acute hepatitis or HCC had a similar prevalence of anti-HCV as healthy individuals. However, 34% of the adult patients with chronic hepatitis/cirrhosis showed signs of a HCV-infection. When the data were analysed with respect to modes of viral transmission, crowding, transmission by unsafe sexual practice or contaminated injection material, and to a lesser extent vertical transmission, seem to be relevant for HBV. The main mode of acquiring HCV infection is probably through medical injections of all sorts, a habit which is very popular in Takeo. Prophylactic measures should concentrate on the prevention of HBV and HCV infections by hygienic means. HBV mass vaccination should be considered in the future.