Accidents are hazards to which health workers are exposed. Hazards may be physical, chemical, biological, mechanical or psychosocial. Mechanical hazards are very common in the health industry because of the frequent use of pointed and sharp instruments such as needles, scalpel and knives. This six-month (June 1999 and June 2000) longitudinal incidence study was carried out at the Central Hospital, Benin City, Nigeria, as a follow-up on a previous cross-sectional study on frequency of blood-related work accidents in the same hospital. All the doctors, laboratory workers and 50% of nurses were included in the study. The nurses were selected using stratified random sampling method. Two hundred and fourteen health care workers started the follow-up study, out of which 146 were left at the end of the six-month period, giving an attrition rate of 31.8%. Results shows that contact with patients' blood with ungloved hands, blood splashes on the face and other parts of the body, needle pricks, cuts from drug ampoules and glove perforation during surgery were the major work-related accidents/injuries during the six-month follow-up. This is similar to findings from the retrospective study. The frequencies of various accidents were higher during the six-month follow-up (incidence study) than the six months prior to the study (retrospective study). Combining all the health workers, the incidence densities of these five major work-related accidents were between 3.6 per person years (ppy) to 9.5ppy. These incidence densities were all significantly higher for doctors than nurses or laboratory workers. There is an urgent need to reduce the incidence of these work-related accidents/injuries in order to reduce the chances of health workers developing occupationally acquired diseases.