Four men with evidence of hemiatrophy resulting from early-life hemispheral injury developed unilateral hemiparkinsonism on the side of the hemiatrophy. The parkinsonism began in the 4th decade and has remained unilateral for 5-35 yr. In all 4 patients, the parkinsonism was slowly progressive, but the clinical response to L-dopa was minimal, suggesting that the parkinsonism might have a postsynaptic striatal component. The clinical similarities of these 4 patients suggest that this is a distinct syndrome in which hemiparkinsonism is a late sequela of hemiatrophy. Identification of this syndrome has prognostic significance, because it seems to have a stereotyped course, remaining unilateral and only slowly progressive.