[Pathological laughing and posterior fossa tumours (author's transl)].

Posterior fossa tumours give rise, sometimes, to psychiatric disturbances, which are difficult to diagnose, when they are isolated without any neurological signs. This was the case in our report of a 32-year-old man who had a pathological laugh, unique symptom, during 4 months, of a trigeminal neurinoma. Spasmodic laughs related to posterior fossa tumours are infrequently reported in the literature. They always are the sign of a pseudo-bulbar syndrome, due to a bilateral lesion of the cortico-bulbar tracts. Other involuntary laughs are encountered in third ventricle's lesions, in frontal lobe lesions and in epilepsy.