We determined the prevalence of hepatitis B markers and the compliance to hepatitis B vaccination in a University Hospital of Santa Maria, Lisbon. The program was begun in 1989 for all hospital personnel and students of the medical school. The screening included 2,360 health care workers and 1,153 students; 57% (2,360/4,103) of hospital personnel and 41% (1,153/2,779) of medical students appeared for vaccination. The prevalence of hepatitis B markers was 16.8% (397/2,360) for hospital personnel and 5.5% (64/1,153) for students, the chronic carrier appearing in 0.95% (22/2,360) of hospital personnel and 0.3% (4/1,153) of students. The departments with the highest prevalence were the Biochemical Laboratory (64%, 7/11), Surgery (42%, 13/31), Pulmonary (39%, 9/23), Emergency (29%, 7/24), Hematology Laboratory (29%, 7/24), and Orthopedics (29%, 10/35). The prevalence was higher in students in the last 3 years of medical school than those in the first 3 years (12.2% [22/181] vs. 7.2% [8/110], p = NS). Adverse effects to vaccination occurred in 14.5%, with local pain the most frequent in 8.6%. The serologic efficacy was 95% (1,044/ 1,097). A nonresponse was observed in male workers, 13% (26/200) compared with 5% (45/897) for females (p < 0.05). Older employees also showed higher nonresponse: The average age of workers with anti-HBs of 0 IU/l was 52.3 years and those with anti-HBs of more than 100 IU/l was 38.4 years (p < 0.02). Hepatitis B vaccination is safe and effective. Our study shows the need for a more aggressive approach to the vaccination of health care workers because a significant percentage of them are not protected.