Of 251 patients with congenital scoliosis, occult congenital intraspinal anomalies were diagnosed in forty-six (18.3 per cent). A diastematomyelia was the commonest anomaly (forty-one patients). Other less common anomalies, occurring alone or in association with a diastematomyelia, were: neurenteric, epidermoid, and dermoid cysts; teratoma; lipofibroma; absence of nerve roots; fibrous bands; and a tight filum terminale. Intraspinal anomalies were associated with all types and sites of congenital scoliosis by far the highest incidence (52 per cent) occurred in association with a unilateral unsegmented bar with contralateral hemivertebrae in the lower thoracic or thoracolumbar regions. Thirty of the patients with an intraspinal anomaly had neural abnormalities, which usually affected only one lower extremity, and in twenty-four patients a paralytic foot deformity developed. Neural deterioration occurred in nine of these patients before the age of five years and was halted by excision of the anomaly. An additional twelve patients (4.8 per cent) of the 251 with congenital scoliosis also had a unilateral neural deficit in the lower limb and a paralytic foot deformity, similar to those found in the patients with an intraspinal anomaly, but had no myelographic evidence of a structural anomaly.