Pathologic laughter which usually occurs after bilateral or diffuse cerebral lesions was rarely reported in patients with unilateral stroke. I describe clinical and radiological findings of 13 patients presenting pathologic laughter due to unilateral stroke. Their laughter was excessive, unmotivated, uncontrollable and most often occurred during conversation especially at the initiation of speaking. There usually was a latent period between the onset of stroke and occurrence of the pathologic laughter. The degree and duration of the pathologic laughter varied, but its severity tended to diminish during the follow up. Some of them also had emotional instability evidenced by easy weeping. Imaging studies showed that 12 patients had infarcts and one had a haemorrhage. The lesions were located in the lenticulocapsular area in 8, pontine base in 3, thalamocapsular area in 1, and cerebral cortical-subcortical area in one. The lenticulocapsular stroke usually involved the upper part of the basal ganglia and a genu or an anterior portion of the posterior limb of the internal capsule/corona radiata. In conclusion, unilateral, usually subcortical, strokes can produce pathologic laughter. Although the neuroradiological data presented here generally support the motor release hypothesis, the delayed onset symptoms suggest that more complex mechanisms may be involved.