We have extended the study of a previously published kindred with spastic paraplegia and palmoplantar hyperkeratosis from 2 to 18 persons. Present evidence suggests that both neural and cutaneous manifestations are due to a single mutant gene, inherited as an autosomal dominant. Nerve conduction and EMG examination provide evidence for mild lower motor and primary sensory neuron (axon) involvement but these techniques are not useful for early detection. The disorder is a unique genetic disease which stands apart from other mostly recessively inherited varieties of neuroichthyosis.