About two percent of the population suffer from Obsessive Compulsive Disorder (OCD; Rapoport, 1989). It has been postulated that OCD is caused by a cortical dysfunction and a disinhibition of subcortically programmed stereotypies (Schwartz et al., 1996). Within the framework of an evolutionary concept of brain development, compulsions may be interpreted as the manifestation of phylogenetically obsolete behavior patterns that are no longer under the control of cortical brain centers (Jackson, 1927). This hypothesis may help to explain similarities between compulsions and ritualistic behavior in so-called primitive cultures. To assess the plausibility of this hypothesis, current neurobiological findings on the pathogenesis of compulsions and stereotypic movements are reviewed and contrasted with anthropological descriptions of cultural rituals. A phenomenological tradition within psychiatric psychopathology discriminates between obsessions, compulsions and "compulsive impulses." Obsessions are intrusive thoughts or images that, unlike the schizophrenic first rank symptom of thought insertion, are not felt to be caused by an outside agent (Fähndrich, 1981). Compulsive rituals are often carried out to ward off negative consequences of aggressive or obscene obsessions. Patients are, however, aware that these compulsive activities are irrational, useless or exaggerated (American Psychiatric Association, 1995). For instance, a female patient experienced the obsessive thought that God and the devil have intercourse, which intruded in a very drastic way. Although not particularly religious, the patient was shocked, retreated into an unobserved space and performed a ritualistic prayer to compensate for the blasphemy thought. With increasing frequency of the obsessive thought and compensatory ritual, she was ultimately unable to perform activities of daily life. Compulsive impulses are phenomenologically placed between obsessions and compulsions. On the one hand, they are mental phenomena experienced by the patient, and are accordingly classified as obsessions by the American Psychiatric Association (1995). On the other hand, the impulses may induce simple behavior patterns. A typical example is coprolalia, the urge to utter curses when stressed (Fähndrich, 1981). This paper will specifically examine current findings on the pathogenesis of Gilles de la Tourette Syndrome (GTS). GTS is a hereditary neuropsychiatric disorder characterized by motor and vocal tics and the frequent manifestation of obsessions and compulsions (Cummings and Frankel, 1985; Lajonchere et al., 1996). The co-occurrence of tics and OCD has stimulated the search for a common neuropathological correlate of both syndromes. Genetic studies support the notion of a spectrum disorder that may manifest as simple tics, “pure” obsessions and compulsions or GTS (Swedo and Leonard, 1994; Hyde and Weinberger, 1995). GTS has been called a model neuropsychiatric disorder (Hyde and Weinberger, 1994), which allows the examination of the pathogenesis of simple motor tics as well as the more complex obsessions and compulsions.