Of the 169 human immunodeficiency virus (HIV)-infected children being cared for at Siriraj Hospital from January 1998 to September 2000, 10 had Mycobacterium avium complex (MAC) infection; seven had disseminated disease and three had MAC pneumonia. Nine children were in the advanced stage of HIV disease at the time of diagnosis with the median CD4 count of 7 cells/mm3 and 127 cells/mm3 and the median age of 65 months and 63 months in disseminated MAC and MAC pneumonia respectively. None of these children had received prior chemoprophylaxis. Common clinical findings included prolonged fever, weight loss, lymphadenopathy, hepatosplenomegaly, diarrhea, anemia and leukopenia. The outcome of MAC infection was poor, with a mortality rate of 60 per cent. In in vitro susceptibility testing, clarithromycin was the least resistant drug. With the incidence rate of 2.15 per 100 person-years, the high rate of antimicrobial resistance, and the poor outcome, primary chemoprophylaxis for MAC infection in conjunction with effective antiretroviral therapy should be considered for Thai children in the advanced stage of HIV infection.