summary A 22-year-old man sometimes engaged in inappropriate laughter. The affective lability fitted in with the diagnosis of mental retardation and of a personality disorder Not Otherwise Specified. In this brief review of the literature we discuss the neuroanatomy, psychodynamics and phenomenology of pathological laughter. Up till now there have been only a few restricted and fragmentary studies of pathological laughter in psychiatry. Pathological laughter is often a result of organic mental disorders.