The frequency of nine reactivating or opportunistic infections and Kaposi's sarcoma among patients with the acquired immunodeficiency syndrome (AIDS) was reviewed. The diagnoses of 87 patients reported from the Colorado AIDS registry and 359 others from literature reports were abstracted, and data were placed in one of 11 categories on the basis of the risk group of the patient. Pneumocystis carinii infection was significantly commoner among blood or blood-product recipients than among natives of the tropics (P < .001). Tuberculosis and toxoplasmosis each were significantly commoner among natives of the tropics than natives of developed countries (P <.001), whereas disseminated Mycobacterium avium-Mycobacterium intracellulare infections were present more often in the latter group. Among natives of the tropics treated in developed countries, cytomegaloviral infection was diagnosed significantly less often (22%) than among persons from developed countries in whom sexual transmission was presumed (47%; P = .0005). These data suggest that the pattern of infections manifested in AIDS could provide clues about transmission and that there may be a hierarchy of reactivation of latent infections in which populations with exposure to multiple agents manifest these preferentially to Pneumocystis carinii.