In a 10-year dynamic cohort study, 976 health care providers were followed a mean of 1.9 years to evaluate the risk of human immunodeficiency virus (HIV) transmission, delayed seroconversion, and seronegative latent infection following occupational exposures. The seroprevalence and incidence of HIV, hepatitis B virus (HBV), hepatitis C virus (HCV), and cytomegalovirus (CMV) infection were also measured, with annual serologic testing for viruses and postexposure HIV tests. One of 327 percutaneous exposures (0.31%; confidence interval, 0.008%-1.69%) and 0 of 398 mucocutaneous exposures to HIV-infected blood transmitted HIV. Neither delayed seroconversions nor seronegative latent infections were detected. The baseline seroprevalences of HBV, HIV, HCV, and CMV infection were 21.7%, 0, 1.4%, and 43.4%, respectively. Corresponding incidence density rates were 3.05, 0.055, 0.08, and 2.48 (per 100 person-years). Despite infection control precautions and availability of hepatitis B vaccine, these health care providers remain at risk for acquiring bloodborne viral infections.