During a 22-month period, we identified 39 patients with human immunodeficiency virus (HIV) infection (mean CD4(+) count, 90 cells/mm(3)) who were hospitalized with pneumonia and who had sputum and/or other specimens that tested concurrently positive for both Mycobacterium tuberculosis and Pneumocystis carinii. The most common chest x-ray abnormality was a reticulonodular pattern or bilateral infiltrates (n=26). Serum lactate dehydrogenase levels were elevated in 17 (85%) of 20 of patients tested (mean value, 2208 U/L). Mean O(2) saturation and PO(2) were 89% and 64 mm Hg, respectively. A majority (24 patients [62%]) received both antituberculous and anti-PCP therapy (17 with steroids), and 22 improved. All ten patients who received no treatment for PCP improved and were discharged from the hospital, whereas 4 (80%) of the 5 persons who received no antituberculous treatment had a poor outcome (P<.001; OR=43). Patients with HIV or acquired immune deficiency syndrome may present with both TB and PCP; of the 2, TB seems to account for the most severe features of disease.