This paper presents 6 patients with catatonia and subthalamic mesencephalic tumors with hydrocephalus involving the third and the lateral ventricles. This anatomic and psychiatric anomaly is investigated on the basis of personal observations and a review of the literature. These cases allow an interesting parallel to be traced between neurological clinical signs and psychiatric signs. Various anatomic and physiological models are discussed which emphasize specialized neuronal circuits (somewhat similar to those involved in Parkinson’s disease) and certain specific neurotransmitters such as dopamine, together with the reactivity of these circuits to intracranial pressure variations. Once more, clinical and laboratory data on schizophrenia concur to suggest that organic etiology is the causal factor in a known psychiatric patholog