Between January and August 1999, a total of 7277 blood donors at various health centers in Kinshasa, Democratic Republic of the Congo were screened for human immunodeficiency virus 1 (HIV1) and hepatitis B surface antigen (HbsAg) using the ELISA technique. Findings showed an incidence of 6.4% for HIV1 antibodies, 9.2% for HbsAg, and 1% for HIV1 and HbsAg. Young females (under 39 years of age) from lower socio-economic classes were the most likely to be infected by HIV1. The risk of HIV transmission by transfusion of contaminated blood was 3%, which is close to the incidence of HIV in the general population. The findings of this study document the need to speed up implementation of blood donor screening in the city of Kinshasa and the rest of the country.