Cyclic neutropenia (CN) is a rare hematologic disorder characterized by regular cycling of the absolute neutrophil count and a symptom complex presenting during the neutropenic nadirs. Despite the profound cyclic neutropenia, most patients have a benign course of recurrent fever, malaise, oral ulceration, and minor skin and upper respiratory tract infections. Recurrent infections, inflammation, and ulcers can lead to significant chronic morbidity. Severe dental disease is common, pregnancy complications are increased, and overwhelming infections, bowel necrosis, and mortality, although rare, are potential sequelae. We report a 10-year-old boy with a classical presentation of CN that had remained undiagnosed for 10 years. The difficulty in diagnosing this unusual disorder is highlighted. Treatment with daily recombinant granulocyte colony-stimulating factor (rG-CSF) resulted in a complete clearing of symptoms and a significant increase in quality of life. The excellent clinical response of CN to rG-CSF, in the absence of major adverse effects, is strongly demonstrated by this case and supports rG-CSF as a first-line therapy for CN. The physiologic and adverse effects of rG-CSF use in CN and other neutropenic disorders, including potential leukemic induction, are reviewed. The need for long-term follow-up to investigate the effects of chronic hematopoietic stimulation by rG-CSF is emphasized.