This study reports the course of measles and results of measles immunization in a cohort of human immunodeficiency virus-infected children. Six cases of measles were identified. All had typical clinical manifestations, 5 of 6 developed pneumonia and 3 of 6 died. A measles intervention program consisting of serologic screening and active immunization (measles-mumps-rubella (MMR)) was instituted in 1990. Among 127 children with data available for analysis (mean age, 6.7 years), only 35% had documentation of prior immunization with MMR. Among 80 children who had preimmunization measles serology reported, 56% were measles antibody-negative and 40% were antibody-positive; following intervention 36% remained measles antibody-negative. Six children lost measles antibody over time. MMR nonresponders had lower CD4 lymphocyte counts (303 +/- 394) compared with responders (865 +/- 677; P = 0.0058). Measles is a potentially fatal illness in human immunodeficiency virus-infected children. Prevention strategies are limited by low rates of age-appropriate MMR immunization, poor antibody responses to MMR in older human immunodeficiency virus-infected children and seroreversion.