To determine the prevalence of HBsAg among blood donors in Ilorin, in the middle belt area of Nigeria.Cross sectional.University of Ilorin Teaching Hospital.100 patients from antenatal clinic, 100 patients from STD clinic and 295 healthy blood donors from UITH.Prevalence of HBsAg.One hundred and sixteen (23.4pc) of the subjects were positive for HBsAg. These included 16pc of ANC patients, 36pc of STD patients and 21.7pc of blood donors. The positivity rate among STD patients was significantly higher than among ANC patients (p < 0.01) and blood donors (p < 0.01). The positivity rate among patients above 34 years of age was higher than in those of 15 to 34 years.The above positivity rates are higher than those previously reported in Nigeria and may indicate increasing prevalence. The highest rate found among STD clinic patients may have identified them as a reservoir group to which control programmes need to be targeted.