There is an extensive behavioural neurological literature on so-called unilateral attentional disorders, but a striking paucity of papers on global disorders of attention, i.e. confusional states. However, confusional states are distinctive because: (1) they are the most common disturbance of the higher functions in clinical practice, by orders of magnitude; (2)they are the only disturbance of the higher functions from which all normal subjects have suffered; (3) they have characteristic clinical manifestations; (4) they are frequently misdiagnosed as progressive dementias, aphasia, memory disorders, and psychoses; (5) they are the only disturbance of the higher functions that commonly cause patients to produce statement that appear to be extremely witty; (6) they can be readily studied experimentally; (7) they are the most common cause of unconcern with or denial of illness. There are almost certainly several different forms of confusional state depending on the aetiology, the rate of development, the age, and the anatomical systems involved, but little classification has yet been carried on. Confusional states are most simply defined as disorders in which there is a loss of the normal coherence of thought or action. Among the striking clinical features are: (1) failure to pay attention, excessive distractibility, or failure to shift attention; (2) paramnesias, i.e. distortions of memory; (3) reduplicative phenomena, 'wild' paraphasias with 'propagation' of error, alterations of mood in many different directions; (4) isolated or predominant disturbance of writing (the most common cause of pur agraphia); (5) unconcern with or denial of illness; (6) apparently playful behaviour. While confusional states are usually attributed to 'global involvement of the brain' as a result of metabolic or toxic disorder, there are in fact many cases produced by focal infarctions inthe right hemisphere, which, in the experience of my department, is one of the commonest effects of cerebrovascular disease. Brief reference is made to the prognosis, and to the theoretical significance for cerebral dominance and the evolutionary development of cerebral dominance in non-human species.