Patient characteristics and clinical course are described in 21 children with newly discovered neutropenia (absolute neutrophil count less than 1500/microliter). Only children over age 3 months are included; 19 of 21 were less than age 2 years. The majority had respiratory tract infections and 11 had been on various medications at the time neutropenia was discovered. Bacteria were isolated from the blood of three patients (S. pneumoniae in two, H. influenzae in one) and from urine in one (E. coli). Respiratory syncytial virus was cultured from the nasopharynx of two patients. Opportunistic, gram-negative and staphylococcal infections did not occur. Neutrophil counts in all but one child returned to normal within 6 weeks of onset; half recovered within 7 days. Bone marrow examination was performed in 13 patients: maturation arrest at various stages in the myeloid series was noted in six, and seven had normal myeloid maturation. Bone marrow findings did not correlate with degree or duration of neutropenia. These observations indicate that previously well infants with isolated neutropenia generally have a benign clinical course, although three patients were ultimately proven to have significant chronic illness. Recommendations are made as to management.