PIP: Knowledge of the survival times of patients with acquired immunodeficiency syndrome (AIDS) and the factors that influence survival is important both for increasing understanding of the pathophysiology of the disease and planning health service interventions. Although there is considerable variation in survival after AIDS diagnosis, even within developed countries, most studies have estimated a mean survival time of 12-18 months. Those with a higher CD4 lymphocyte count at initial diagnosis have a more favorable prognosis. Diseases such as Kaposi's sarcoma, tuberculosis, and lymphoma (tending to be associated with higher CD4 levels) are less likely to be fatal than opportunistic infections such as cytomegalovirus disease and Mycobacterium avium complex. The initial AIDS-defining illness and the number and type of subsequent AIDS-related infections are also strong predictors. A recently proposed staging system for patients with AIDS, based on a score that takes account of the CD4 count and the number and type of AIDS-defining illnesses, has been validated in two cohorts of patients. Patients treated with zidovudine also show improved survival; however, this effect may be temporary. Without controlling for other variables such as access to health care, some studies have found decreased survival time in older persons, minority ethnic groups, women, intravenous drug users, and those from lower socioeconomic groups. When controls are introduced, however, there is no longer evidence of an association between prognosis and gender, ethnic origin (within developed countries), or exposure category. Due to factors such as widespread use of antiretroviral therapy, primary prophylaxis against pneumocystis carinii pneumonia, and more efficient treatment of other opportunistic infections, there has been a recent trend toward increased AIDS survival times.