This study focused on the risk factors for hepatitis B virus infection in Kamphaengphet hospital personnel during April 1, 1989 to May 31, 1989. The target groups were Janitors, Nursing-Aids, Laboratory technicians, X-ray technicians, Assistant nurses, technical nurses, Registered nurses, Doctors, Dentists, Dentical nurse and Assistant dentists, particularly those who work in Out Patient Department, Opthal clinic, Emergency room, Operating room, Laboratory-blood bank, Dental clinic, Center of supply, laundry unit, Nutritional unit, Radiative unit, Social medicine unit, Medicine and Surgery (man), Medicine and Surgery(girl), Surgery(man), Obstetrics, Pediatrics, clergy ward, Special ward. Personal histories, obtained through self-administered questionnaire, and blood samples were taken from every personnel. Serum samples were examined for HBV markers (HBsAg, Anti-HBs, Anti-HBc) in laboratory unit of Kamphaengphet hospital by RPHA and PHA techniqres. Out of 326 persons in the target group, blood samples and completed questionnaires wer obtained from 298 respondents (91.4%). In 298 persons, there were 42 males (14.1%), 256 females (85.9%), over all HBV infection was 53 percent, carrier (HBsAg, HBsAg + Anti-HBc) 8.7 per cent, Anti-HBc 20.8 per cent. Immuned persons (Anti-HBs, Anti-HBs + Anti-HBc) constituted 23 per cent of the target population. Family income per month of less than 10,000 baht, age groups of 30-34 and over 40 years, working period of more than 10 years, past history of blood recipients, heterosexual experience, and married status were factors that significantly associated with HBV infection. The results suggested that horizontal transmission acquired both inside and outside hospitals played significant roles in the HBV infection among hospital personnel. In order to be able to strengthen effective prevention and control of HBV infection in Thai population, horizontal trandsmission, via blood transfusion and sexual intercourse must be considered. On the basis of this study, vaccination of adults is also recommended whenever possible.