The application and critical evaluation of brain-computed tomography (CT) to psychiatry are presented primarily in relation to the cerebral atrophies and organic brain syndromes. It can be observed, that clinical diagnosis of brain atrophy is frequently made only upon findings of diffuse cortical atrophy. The attention is directed to the non-consistent CT scan measures and diagnostic criteria of brain atrophy on CT scan due to non-consistent methodologies of sulcus and ventricular measurements. The linear and planimetric measurements and difficulties in exact analysis of cerebral atrophy on CT scanning are discussed. The nosology, clinical criteria and etiology of chronic organic brain syndromes, the clinical conditions and diseases connected with diffuse cerebral atrophy noticeable on CT scan are reported. The conclusion is, that diffuse cerebral atrophy on CT scan without clinical symptoms and criteria of cerebral atrophy cannot be considered as basis for making psychiatric diagnosis, respectively, that such finding needs other exact clinical, psychiatric and psychological examinations.