A three-month-old girl presented with a massive abdominal tumour arising from the right lumbar region. Microscopic examination of a biopsy specimen showed a typical neuroblastoma. No treatment was given except that necessary symptomatically for paralysis caused by compression of the cauda equina. Spontaneous regression was accompanied by maturation to a small ganglioneuroma, found at necropsy examination at the age of ten years. Death was from urinary infection due to a persistent neurogenic bladder.