New highly active antiretroviral therapies are boosting the blood absolute CD4+ counts of many patients with AIDS and are decreasing the prevalence of AIDS-related opportunistic infections. Nevertheless, the prevention, diagnosis, and treatment of opportunistic infections remain important features of management of HIV infection. In recent years, significant advances have been made in the prevention and treatment of opportunistic diseases such as Pneumocystis carinii pneumonia, Cytomegalovirus retinitis, disseminated Mycobacterium avium-intracellulare infection, and mucosal candidiasis. Tuberculosis, cryptococcal meningitis, herpes simplex virus infection, shingles, and infectious enteritis also continue to be troublesome. Kaposi's sarcoma may be the newest AIDS-related opportunistic infection to be identified. The immune system effects of highly active antiretroviral therapy are as yet Poorly understood. Therefore, an aggressive approach to diagnosis and treatment of opportunistic infections remains mandatory, and patients receiving antiretroviral therapy should continue to adhere to recommendations for prophylaxis against such infections.