OBJECTIVES: We sought to define the prevalence of tuberculin skin test (TST) positivity in a group of newly hospitalized patients, to identify risk factors for positive tests, and to examine the impact of testing on infection control practices. DESIGN: Unblinded cohort study over 5 days in July 1992. SETTING: A 1,000-bed university-affiliated hospital. PATIENTS: All patients admitted (excluding obstetric patients and newborns) were interviewed. Patients without a history of tuberculosis (TB) or a positive TST were offered a TST with Candida and tetanus controls. RESULTS: Of 346 patients offered the test, 21 (6%) had a prior history of TB or a positive TST, and 36 (10%) declined to participate; 279 of the remaining 289 completed the study. Anergy was demonstrated in 94 (33.7%) of 279 patients. New positive TSTs were identified in 19 (10.3%) of 185 nonanergic patients. Of the 19 TST-positive patients, 6 (32%) had infiltrates on chest radiographs and were evaluated for active TB. One patient was treated empirically for active TB, and five received isoniazid prophylaxis. Risk factors for a new positive TST included age (odds ratio [OR], 1.56 per decade of life; P=.021), African American race (OR, 4.81; P=.008), alcohol abuse (OR, 5.53; P=.005), and peptic ulcer disease (OR, 4.53; P=.017). Risk factors for anergy included admission to a surgical service (OR, 2.1; P=.006), current use of steroids (OR, 2.65; P=.005), and human immunodeficiency virus (HIV) infection (OR, undefined; P=.034). CONCLUSIONS: Despite a high rate of anergy, routine tuberculin skin testing identified a substantial number of patients with TB infection who might otherwise have gone unrecognized.