Hepatitis B is recognized as a major health hazard to hospital personnel. During a four-year period, 30 cases of hepatitis B were attributed to work at an urban medical center. Only four of these 30 individuals described a relevant accident in advance of their hepatitis and five others retrospectively suggested a specific episode that might have accounted for their illness. Early symptoms of the illness were nonspecific and routine monitoring and clinical awareness are necessary for early diagnosis. All employees recuperated from their acute hepatitis, but one developed chronic active hepatitis. The incidence and morbidity of the disease emphasize the need for more effective control measures. The inconspicuous exposures responsible for the illnesses observed render it unlikely that any postexposure immune globulin prophylaxis will suffice in further reducing the incidence of hepatitis B.