‘Cognitive disorders’ is a broad and heterogeneous diagnostic category, which includes different disorders, each with a distinct aetiology. They affect individuals in different ways depending on the age in which they occur. The term may be applied to a child, who has experienced perinatal trauma as well as to an older person with a beginning dementia of the Alzheimer type. The scientific literature on offenders with cognitive disorders is sparse. Most authors in forensic psychiatry do not systematically differentiate between the diagnostic subcategories and tend to use broad terms, such as organic disorder, organic psychosis, organic brain syndrome, neuropsychological deficit, dementia, mental handicap, mental retardation to include a number of different disorders in their studies. The number of patients with any kind of brain disorder in forensic hospitals and institutions is comparatively small and ranges from 1 to 10 per cent of all forensic inpatients. The same numbers apply for individuals assessed for criminal responsibility or risk of reoffending. Compared to major mental disorders like schizophrenia or affective disorders or to personality disorders, patients with cognitive disorders account for only a small proportion of individuals seen by forensic psychiatrists. Subdividing this group any further would be statistically irrelevant. The way forensic psychiatry and the law deals with offenders suffering from organic brain disorders is rather derived from case reports and convention than from empirical knowledge.