Early medical intervention in patients with HIV infection is beneficial even in asymptomatic individuals. Medical care in these patients consists of the use of antiretroviral drugs, drugs to prevent opportunistic infections, vaccines and comprehensive psychosocial support. It is important to determine the stage of the natural history of the disease at any given moment. Besides clinical data, the determination of CD4+ T-lymphocytes is useful to make decisions related to the institution of antiretroviral drugs and preventive therapy for opportunistic infections. Present evidence shows a clear benefit of starting antiretroviral drugs in every patient with AIDS or AIDS related complex and also supports the use of these drugs in early stages of the disease. Preventive therapy against Pneumocystis carinii has to be instituted in every patient with CD4 lymphocyte counts below 200/mm3. Prophylactic therapy may also be necessary to prevent tuberculosis, toxoplasmosis and M. avium. It is likely that future studies will show some benefit with the use of additional preventive strategies for other frequent infections such as Cytomegalovirus and Cryptosporidium.