A patient with polymyositis responded initially to steroid therapy. A muscle biopsy disclosed features of primary myopathy and group atrophy. The patient became refractory to therapy and died with relentlessly progressive weakness. The autopsy disclosed lower motor neuron involvement and degeneration of the spinocerebellar tracts. There was loss of Purkinje cells, which may have occurred secondary to an anoxic episode prior to death. The case is unique because of the limited involvement of the lower motor and spinocerebellar systems.