Between 1981 and 1991, disseminated nontuberculous mycobacterial infection (DNTM) was reported in 199 (5.7%) of 3472 children less than 13 years of age with acquired immunodeficiency syndrome (AIDS) in the United States. More than 85% of DNTM cases were caused by infection with Mycobacterium avium complex. The proportion of AIDS cases with DNTM was higher in those with hemophilia or transfusion-associated human immunodeficiency virus (HIV) infection than in those with perinatally acquired HIV infection (12.9% and 13.8% vs. 4.6%; P < 0.001). The proportion of AIDS cases with DNTM did not differ significantly by sex (6.1% in males and 5.3% in females) or race (7.4% in whites, 5.0% in blacks and 5.5% in Hispanics) when stratified by HIV transmission category. An active HIV infection surveillance project in 6 geographic areas revealed that the median age at diagnosis of DNTM was 3.3 years for perinatally acquired HIV infection but 8.7 years for DNTM in children with hemophilia or AIDS associated with transfusion, presumably because many of the latter acquired HIV at an older age. Among children with DNTM who had CD4 counts performed within 6 months of the date of DNTM, the median was 17 cells/mm3 and 70% of cases of DNTM occurred in children with fewer than 50 CD4 cells. We conclude that clinicians should have a high index of suspicion for DNTM in children with lower CD4 counts and a longer duration of HIV infection and that preventive strategies, such as prophylactic antimycobacterial therapy, should be focused on this group of children.