A 48-year-old white man (index case) with an abnormal chest radiograph remained undiagnosed for tuberculosis for 4 years. Investigation by purified protein derivative (PPD) tuberculin test revealed positive tuberculin reactions (> or = 10 mm induration) in seven of eight (88%) initial close contacts, and in 12 of 46 (26%) coworkers. On the suspicion that transmission had also occurred among members of the index case's church congregation, a PPD tuberculin test survey of 184 of 200 of the members revealed 77 (42%) positive reactors. Thirty percent of the members under the age of 35 years were infected, suggesting transmission of infection. Eight cases of active tuberculosis (including the index case) were detected, yielding a high case rate (4.3%) among the parishioners. Three of the cases were confirmed recent PPD converters. Although bacteriologic findings were available in only three of the eight cases, two cases had phage typing of organism identical to the index case; the third had recrudescent tuberculous disease. Of the remaining five cases without bacteriologic confirmation, two had pleural tuberculosis, one child had progressive primary tuberculosis, and two persons had localized pulmonary nodules suggestive of primary infection progressing to disease. Because transmission of tuberculous infection may occur in any closed environment, including a church, physicians must be conversant with tuberculosis control measures and preventive therapy guidelines to preclude unforeseen transmission of disease.