We report 5 cases of complete, or nearly complete, agenesis of the lumbar and sacral spine. In 1 case pregnancy was terminated at 23 weeks of gestation, and the others were livebirths. The surviving 4 patients were all infants of diabetic mothers. Imperforate anus was present in 2 of 4 liveborn patients and was suspected in the abortus. All liveborn cases were paraplegic, and all exhibited the 'Buddha' deformity of the lower extremities. One patient had congenital obstructive hydrocephalus, probably representing a variant of holoprosencephaly, requiring a ventriculoperitoneal shunt. No other nervous system anomaly was identified in any patient, and the other patients are showing normal cognitive development. We propose that these patients have defects which occurred during germ cell formation (i.e., during gastrulation), with interruption of the primitive streak resulting in combined failure of primary and secondary neurulation.