We describe the clinical and radiologic changes related to progressive facial hemiatrophy (Parry-Romberg syndrome) occurring during a 20-month period in a child who presented with unilateral neurologic deficits and facial hemiatrophy. CT and MR findings included unilateral focal infarctions in the corpus callosum, diffuse deep and subcortical white matter signal changes, mild cortical thickening, and leptomeningeal enhancement with dense mineral deposition. Angiographic findings were normal. We hypothesize that a noninfectious, unilateral inflammatory process, possibly associated with a chronic vasomotor disturbance and sympathetic nerve chain inflammation, was a major factor in the pathogenesis of this syndrome.