- Background: Acquired neutropenia in immunocompetent children is common, and its differential diagnosis ranges from benign causes to life-threatening diseases. We described the etiology, clinical picture and outcome of new-onset neutropenia in immunocompetent children assessed in the emergency department and hospitalized at our medical center. Methods: Previously healthy children admitted with neutropenia (absolute neutrophil count <1.5 × 109/L) were included. Serious bacterial infections were defined as culture-positive blood, urine, cerebrospinal fluid, articular fluid or stool infections, pneumonia, Brucellosis and Rickettsiosis. Results: A total of 601 patients (5 days–202 months old) were enrolled; 3 (0.5%), 48 (8%), 165 (27.5%) and 385 (64%) had absolute neutrophil counts <0.2, 0.2–0.5, 0.5–1.0 and 1.0–1.5 × 109/L, respectively. Associated leukopenia and thrombocytopenia were diagnosed in 186 (39%) and 71 (11.8%) patients. Three hundred sixteen of 601 (52.6%) and 519 of 601 (86.4%) were <2 or 36 months of age, respectively. Fever at admission was present in 27.6% patients. Serious bacterial infections were diagnosed in 106 (17.6%) patients. Brucellosis and rickettsiosis were diagnosed in 8 of 52 (15.4%) and 9 of 39 (23.1%) tests obtained. Respiratory syncytial virus was diagnosed in 17 of 33 (51.5%) nasal washes. An infectious etiology was determined in 171 (28.5%) patients. Acute leukemia was diagnosed in 6 patients. A significant correlation was found between resolution of neutropenia and patient age, infectious etiology and severity of neutropenia. Conclusions: (1) Severe neutropenia was rare; (2) More than half of patients were <2 months of age; (3) An infectious etiology was diagnosed in a high number of patients, and serious bacterial infections were frequent and (4) Brucella spp. and rickettsial infections were frequent etiologies associated with neutropenia in our setting.