Forced laughter generally occurs in bilateral or diffuse lesions of the brain and is generally associated with pathologic crying. We report the cases of 3 patients in whom temporary forced laughter occurred after unilateral supratentorial infarction demonstrated by CT scan or MRI. In all cases, the lesion was exclusively subcortical and involved the striatocapsular region. For all patients the laughter occurred during the recovery phase of motor deficit and was 'pure' without associated weeping or other clinical features of pseudobulbar palsy. In all cases, the laughter attacks had become much less frequent or had totally disappeared 1 or 2 months after the stroke. According to a 'motor' hypothesis, a unilateral striatocapsular lesion may lead to temporary deregulation of the expression mechanisms.