The prevalence of Hepatitis B Virus (HBV) markers was studied in 350 staff members from a Psychiatric Hospital, where a high prevalence of HBV markers was observed among patients. The prevalence of HBsAg, anti-HBs plus anti-HBc, anti-HBc alone and anti-HBs alone were determined to be: 2%, 15.1%, 4% and 0.3%, respectively. The prevalence of HBV markers was greater (although not significant) among women (24.7%) as compared to men (17.8%) (p greater than 0.05), and in the personnel with more than 20 years of employment (24.1%), as compared to those with less than 20 years (20% (p greater than 0.05). The highest prevalence of infection was observed in the department in which were admitted children and young adults. The overall prevalence of HBV markers was higher among staff members than in the blood donors of our area. Hospital personnel must know such epidemiologic conditions: active immunization with the Hepatitis B vaccine must be offered to hospital employees, firstly in those institutions in which a high prevalence of HBV infection has been documented.