A case is reported of a spinal subdural hibernoma arising in the lumbar region of a boy aged I4 years who also had a lumbar spina bifda. The circumscribed and encapsulated tumour was attached to the leptomeninges, extended into the d u d sac and compressed upon the cauda equina. Severe pain in the calves was relieved after extirpation of the mass. The pathogenesis of the tumour is suggested to be associated with aberrant differentiation of the mesenchjme or its derivatiws towards aclbose tissue.