A 1‐year‐old male infant showed cerebellar signs and symptoms, and excess urinary excretion of vanillylmandelic acid (VMA). Each of them disappeared spontaneously but a large abdominal tumor occurred at 3 years of age. Surgical specimen of the tumor was diagnosed as neuroblastoma and the patient died at 4 years of age. Autopsy revealed the huge tumor originated from the right adrenal, and occupying the retroperitoneum, pelvic cavity and posterior mediastinum. Histology of the primary lesion was chiefly that of ganglioneuroma, while all of the metastatic ones neuroblastoma. Transitional histology from neuroblastoma to ganglioneuroma was also observed in the primary lesion. The diagnosis was designated as composite ganglioneuroblastoma. The surgical material of the metastatic neuroblastoma was cultured for 2 monthsin vitroand the tumor cell clumps extended spontaneously abundant long neurites. This phenomenon suggests the high maturation ability of the neuroblastoma ce