Reported here are three cases of pulmonary Mycobacterium xenopi infection that occurred in AIDS patients in Hungary shortly after starting highly active antiretroviral therapy. In this country, Mycobacterium xenopi is the most common nontuberculous mycobacterial species causing pulmonary mycobacterial infections. Cases of pulmonary Mycobacterium xenopi disease have been described in patients infected with the human immunodeficiency virus infection and in patients with other immunodeficiencies; however, only limited information is currently available concerning the connection between nontuberculous Mycobacterium infection and AIDS in Hungary. This report thus adds useful information regarding the diagnosis, clinical course, and treatment regimens of Mycobacterium xenopi infections in AIDS patients.