Chronic ambulatory peritoneal dialysis (CAPD) is a commonly used form of renal replacement therapy in patients with end-stage renal disease (ESRD) infected with the human immunodeficiency virus (HIV). An increased incidence of peritonitis, as well as an increased rate of infections with unusual and serious organisms, has been reported in these patients. We report the first case of an HIV-infected patient who developed clinical peritonitis associated with Mycobacterium avium-intracellulare (MAI) infection. We suggest that the diagnosis of MAI peritonitis be suspected in HIV-infected patients with clinical CAPD peritonitis, negative cultures for bacteria or fungi, and a CD4 count less than 100 cells/microL. Therapy with a two-drug regimen for disseminated MAI infection without removal of the peritoneal dialysis (PD) catheter appears to provide symptomatic improvement while allowing ongoing PD.