Cavum Septi pellucid (CSP), a cavity between the laminae of the septum pellucidum, for a longer period has been reported as an anomaly of the brain midline, associated with neuropsychiatric diseases, mostly schizophrenia, but also posttraumatic stress disorder, De la Tourette disease, and persons who survived a repeated a serious head trauma, boxers on the first place. Our investigation has been performed on 479 unfixed frozen brains, of the autopsied individuals of both genders, and MRI scans of 250 examinees, out of which 110 had neuropsychiatric illness. In our sample, the prevalence of CSP was 22.96% among the autopsied individuals and 9.2% in examinees who underwent MRI scan. The cause of the death among schizophrenia suffering persons was suicide (18 out of 25 patients). Obviously, CSP is more frequently associated with neuropsychiatric diseases, but a dilemma still exists, did we make a bias in brain suitability for the examination or we did the same mistake in observing clinical cases. A large CSP, though, is an almost certain sign for an underlying neuropsychiatric impairment, especially schizophrenia. The CSP among alcoholics and persons with the priory sustained head blows is probably of the same cause and represents an aftermath of the diffuse axonal injuries, i.e. brain trauma.