OBJECTIVES This study describes the costs and outcomes of community-based tuberculin screening programs conducted between 1987 and 1991 in Montreal, Quebec, Canada. METHODS Follow-up information was abstracted from hospital records of all reactors detected in tuberculin screening of students in grades 6 and 10, of first-year health professional students, and of workers aged 18 to 25 in a number of workforces. Screening costs were estimated directly from survey records, and follow-up costs were estimated from the annual financial report of the Montreal Chest Hospital for 1989/90. RESULTS Of 7669 persons tested, 782 (10.2%) had positive results and 757 (9.9%) were referred to a clinic. Of those, 525 (6.8% of the original 7669) reported, 293 (3.8%) were prescribed therapy, and 154 (2.0%) were compliant. In Canadian dollars, screening cost $5.70 per person tested and $56 per tuberculin reactor detected, but follow-up of reactors accounted for 73% of the total program cost of $13,455 to $18,753 per case of tuberculosis prevented. CONCLUSIONS Because of high rates of patient and provider noncompliance, a tuberculin screening program was much less cost-effective than anticipated. Screening costs must be targeted to the highest risk populations, and compliance with recommendations for preventive therapy must be maximized.