We conducted a population-based case-control study to determine the magnitude of the excess risk of tuberculosis in those infected with the human immunodeficiency virus (HIV) in Seattle-King County, Washington. Patients were 39 of the 54 cases of tuberculosis in white and in black (including Hispanic) men aged 20 through 49 reported to the Seattle-King County Department of Public Health between January 1986 and June 1988. Controls were 34 white and black men of similar age who had tuberculin testing as a condition of employment. Eleven (28 percent) of the 39 patients with tuberculosis and 2 (6 percent) of the 34 controls tested positive for antibody to HIV (odds ratio adjusted for age and race = 6.2; 95 percent confidence interval 1.2 to 31.9). Calculation of the etiologic fashion indicated that 24 percent of the tuberculosis cases in this population of young black and white men were attributable to concurrent HIV infection.