The clinical, electrophysiological, radiological and morphological data of 3 members of a family with autosomal dominant distal spinal muscular atrophy (DSMA) are reported. One patient has the clinical picture of peroneal muscular atrophy with atrophic calves. His father and sister suffer from cramps and fasciculations of the calves with true neurogenic muscular hypertrophy of the calves. The electromyogram and the biopsy specimen are conclusive for motor neuron disease in this family. These findings suggest that the DSMA variant as described by D'Alessandro et al. (Arch. Neurol. (1982) 39: 657-660), concerning benign spinal muscular atrophy with hypertrophy of the calves, has to be considered as a mild manifestation of DSMA.