An investigation of occupational exposure to human immunodeficiency virus (HIV) among health workers in hospitals in Tanzania's Mwanza region raised serious concerns about a lack of protective measures against such risk. Data, including questionnaires and direct observation, were collected during May-September 1993 in 9 hospitals in the region. Among the 403 hospital workers who completed an acquired immunodeficiency syndrome (AIDS)-related questionnaire, 71% had adequate knowledge scores. On the other hand, observation of hospital wards revealed insufficient measures to reduce the risk of HIV transmission (e.g., non-functioning water taps, lack of plastic bags for disposal of soiled linen, widespread shortage of gloves). 9.2% of 623 nurses and 1.3% of 118 doctors and medical assistants interviewed had pricked themselves in the preceding week; 22% of nurses working in labor wards and 25% of those working in operating theaters had pricked themselves in the previous month. Among the 50 laboratory technicians interviewed, 25% had been pricked in the previous month. In addition, more than half of nursing and medical personnel has been splashed, largely by blood and amniotic fluid, in the preceding month. Assuming an HIV prevalence of 20% among hospital patients in Mwanza, the estimated annual incidence of HIV infection due to occupational exposure is 0.27%, with percutaneous exposure contributing 93% of this risk. Among surgeons, this risk is even higher: 0.7% per year. Prevention of pricking accidents through use of double gloving, forceps to remove syringes, and appropriate containers for needle disposal should be a priority to reduce the risk of occupational HIV exposure.