This study was undertaken to evaluate the recurrence risks for sibs of patients with symmetrical spasticity (either quadriplegia or diplegia) in the absence of factors known to cause spastic cerebral palsy (e.g. pre-term birth, perinatal hypoxia). Among 669 children in the West Midlands with spastic cerebral palsy, 24 had symmetrical spasticity and normal birth histories. This group was clinically and genetically heterogenous. Among their 55 sibs, six had a spastic disorder similar to that in the index patient, and one further sib, who had died young, had been mentally retarded. Of particular interest were two families with an autosomal recessive condition of post-natal microcephaly, myoclonic epilepsy and spastic quadriplegia; and one family, and possibly a sporadic case of X-linked athetoid cerebral palsy. The recurrence risk in this series of approximately 1 in 9 suggests that about half the children with symmetrical spastic cerebral palsy and a normal birth history may have a recessive condition.