BACKGROUND--Antimycobacterial therapy for disseminated Mycobacterium avium complex (DMAC) in patients with acquired immunodeficiency syndrome (AIDS) may ameliorate symptoms and decrease bacteremia. However, no studies have demonstrated improved survival in patients with AIDS treated for DMAC. We assessed the effects of treatment of DMAC on the survival of patients with AIDS. METHODS--We retrospectively reviewed records of patients with AIDS and DMAC seen at two San Francisco, Calif, hospitals between January 1, 1988, and January 1, 1990. The treatment group (N = 76) consisted of patients who received 2 weeks or more of antimycobacterial therapy with at least three agents. The untreated group (N = 74) received either no therapy or isoniazid alone. Patients in both groups lived a minimum of 2 weeks after the diagnosis of DMAC. RESULTS--The median survival in the treatment group was 191 days, compared with 80 days in the untreated group. In a multivariate proportional hazards model (N = 145), both treatment of DMAC (relative hazard = 0.34; 95% confidence interval, 0.23 to 0.51) and treatment with zidovudine (relative hazard = 0.54; 95% confidence interval, 0.36 to 0.82) were associated with improved survival. CONCLUSION--Patients with AIDS and DMAC who are treated with antimycobacterial drugs may survive longer than untreated patients. We recommend that a randomized trial be conducted to evaluate the optimal treatment of DMAC.