The objective of this prospective, observational study was to define the natural history of neutropenia in human immunodeficiency virus (HIV) disease. Eighty-seven consecutive patients developing neutropenia (absolute neutrophil count [ANC], <1000 cells/mm(3)) were recruited and closely followed for the duration of the episode. Episodes lasted a median of 13 days, with a mean ANC nadir of 660 cells/mm(3). Presumed or proven infection occurred in 12 (17%) of 71 evaluable subjects, and culture-proven infection occurred only in 6 (8%) of 71. Most of the episodes of neutropenia were brief, mild to moderate in nadir, and self-limiting without complications. Myelosuppressive therapies were implicated in almost all episodes. Serious infections occurred infrequently and were associated with low ANC nadirs but not with duration of the neutropenic episode. Low CD4(+) cell counts also increased the risk of infection complicating an episode of neutropenia.