Tuberculosis is both a nosocomial and an occupational infection. The prevalence of positive tuberculin skin reactions at King Abdulaziz University Hospital, Saudi Arabia, was investigated by testing 298 health care workers. Conventional tuberculin skin testing was performed using 0.1 mL of purified protein derivative injected intracutaneously. After 48-72 hours, induration size was recorded. The prevalence of positive tests (induration > or = 10 mm) was 78.9% overall, 60.0% for Saudi Arabians compared with 81.8% for non-Saudi Arabians (P < 0.01). The mean response size (8.9 +/- 7 mm) for Saudis was also significantly lower than for non-Saudis (13.9 +/- 7 mm, P < 0.001). To enhance the protection of both health care workers and hospitalized patients, effective preventive measures and annual tuberculin testing of health care workers should be considered.