Pathological laughter is exaggerated, uncontrollable, and inappropriate laughter usually unrelated to a true emotion or a congruent mood. "Fou rire prodromique" is a rare form of prodromal pathological laughter of uncertain pathophysiology that heralds an ischaemic neurologic deficit. We report a case of prodromal pathological laughter marking the onset of bilateral capsular genu infarction. T2-weighted cranial magnetic resonance imaging (MRI) showed bilateral capsular genu infarction. There was also a diffusion defect in the same areas on diffusion-weighted imaging (DWI). Although it is known that bilateral subcortical lesions can cause pathological laughter, this is the first demonstration of simultaneous associated bilateral capsular genu infarction on cranial DWI MRI. (c) 2004 Elsevier Ltd. All rights reserved.