PURPOSE: Pompe disease is one of the glycogen storage diseases caused by a deficiency of acid alpha-glycosidase. This enzyme defect results in lysosomal glycogen accumulation in many tissues and shows a various spectrum of clinical features from early infantile hypotonia to mild weakness. For the investigation of the clinical characteristics of Pompe disease, we reviewed 6 cases of childhood Pompe disease diagnosed by muscle biopsy and acid alpha-glycosidase assay. METHODS: We reviewed the medical records of 6 childhood Pompe disease patients in Seoul National University Children's Hospital, retrospectively from January 2001 to October 2006. RESULTS: The age of the symptom onset was 1 month to 11 years(mean 2.2 years) and the diagnosis was made at the age of 8 months to 14 years(mean 5.3 years). The patients showed delayed motor development, motor weakness, hypotonia, cardiomegaly, hypertrophic cardiomyopathy, hepatomegaly, recurrent pulmonary infections but the severity was very diverse. Liver transaminase and CK levels were elevated in all of the patients. Their muscle biopsy showed the characteristic accumulation of purple colored glycogen granules and the degeneration of myofibers. CONCLUSION: Childhood Pompe disease had various clinical features and severities depending on the age of onset, organ involvement and the rate of progression. Enzyme replacement therapy may modify the disease courses, so we need to diagnose earlier for the treatment at an optimal time.