A kindred with dominantly inherited ataxia demonstrated hypertrophia musculorum vera as a phenotypic feature of the disease. The proband had fasciculations, cramps, absent sensory nerve action potentials, an increased creatine kinase level, dramatic enlargement of calf muscles, and a muscle biopsy specimen showing denervation accompanied by true muscle fiber hypertrophy; ataxia and other clinical signs of spinocerebellar degeneration were also present. Other family members displayed progressive ataxia and calf muscle enlargement to varying degrees. Though peroneal atrophy is a more common feature of the familial ataxias, some kindreds may have muscle enlargement simulating the pseudohypertrophy of muscular dystrophy that is due instead to denervation-induced compensatory individual fiber hypertrophy.