We report a case of somnambulism successfully treated with sansoninto. A 55-year-old woman had an initial episode of somnambulism in childhood, which recurred in her early 20s along with development of psychotic manifestations. The patient was hospitalized in a psychiatric hospital with a diagnosis of schizoaffective disorder and coexisting Crohn's disease. At the age of 55, she began to show nocturnal wandering tendencies and we prescribed yokukansan at 2.5 g/day, though the symptoms only temporarily improved. Following a switch to sansoninto at 7.5 g/day, the symptoms disappeared. Based on our experience with this case, we speculate that the Heart component of the five viscera theory in traditional Chinese medicine plays a key role in somnambulism.