Fifty-four cases of familial OPCA (FOPCA) and sixty-three cases of sporadic OPCA (SOPCA) have been gathered from the literature. The data concerning age at onset, duration of the disease, frequency of symptoms and the various localizations of lesions have been evaluated. In comparison with SOPCA, the disease begins earlier in FOPCA and lasts longer (P less than 0.001). The differences in the percentages of clinical manifestations and associated lesions are also significant with regard to the greater frequency in FOPCA of abnormal movements, ophthalmoplegia, spinal symptoms and lesions located in the dentate nucleus and spinal cord, except for the pyramidal tract. The clinical signs and symptoms are reviewed, special emphasis being given to dysphagia and urinary incontinence, their relevance having been underestimated in previous studies. After a critical analysis of the classifications in current use, I conclude that that of Greenfield (1954) remains the most appropriate.