A 6-year-old Japanese girl with acid maltase deficiency showed unusual clinical features of the disease; doll-like face, short stature, hepatomegaly, proximal renal tubular acidosis, but no muscular weakness or hypotonia. Diagnosis of acid maltase deficiency was made based on the following findings of the liver tissue obtained by surgical biopsy: increased glycogen content, presence of glycogenosome, and reduction and some kinetic abnormalities of acid maltase. The enzyme deficiency was also found in the peripheral white blood cells using anti-human acid maltase anti-serum. These findings suggest that the patient had a new variant form of glycogen storage disease with acid maltase deficiency.