Peritonitis due to Mycobacterium avium complex (MAC) infection is uncommon. The risk for MAC in AIDS patients is greatest in those with severely depressed CD4 count. The organs most commonly involved in disseminated MAC infection include spleen, mesenteric lymph nodes, liver, and intestines. The involvement of peritoneum by MAC infection is rare. This is a case of MAC peritonitis in a 26-year-old female AIDS patient who is noncompliant to highly active antiretroviral therapy (HAART). This patient presented with abdominal pain and distension, anorexia, diarrhea, and cough. She was treated with rifabutin, clarithromycin, and ethambutol along with atovaquone for Pneumocystis jiroveci pneumonia prophylaxis and so the patient's condition improved. MAC peritonitis should be considered in a patient presenting with nonspecific abdominal symptoms in the setting of AIDS and low CD4 count.