The clinical features of 40 cases of tumour of the occipital lobe have been reviewed, and their frequency, pathogenesis and significance discussed. The initial symptoms were epileptiform attacks in 30 per cent.; a visual aura or visual hallucinations in 125 per cent.; general mental impairment in 17 per cent.; headache in 35 per cent.; transient or progressive failure of vision in 15 per cent.; and strabismus in 2·5 per cent. In only 12·5 per cent, did the initial symptoms suggest that the visual paths were involved. The relative frequency of different symptoms of tumour of the occipital lobe was as follows : Visual hallucinations, 25 per cent.; symptoms suggesting abnormality of the visual fields, 16 per cent.; epileptiform attacks, 52·5 per cent.; auditory hallucinations, 5 per cent.; abnormal tastes and smells, 12·5 per cent.; headache, 95 per cent.; diplopia, 22 per cent.; impairment of vision, 57 per cent.; disturbances of speech, 35 per cent.; spontaneous subjective sensations, 30 per cent.; disturbances of motor functions, 52 per cent.; and mental symptoms, 55 per cent. Important findings on the examination of the patient were the following: Mental changes, 60 per cent.; contralateral homonymous defects of the visual fields, 94 per cent.; papilloedema or optic atrophy, 70 per cent.; inequality of the pupils, 35 per cent, (contralateral pupil the larger in 25 per cent.) ; ocular pareses, usually of the external recti, 30 per cent.; nystagmus and nystagmoid jerkings, 35 per cent.; disturbances of speech functions, 30 per cent. (50 per cent, of left-sided tumours) ; disturbances of sensation of the suprathalamic type, 55 per cent.; and minor degrees of motor disturbance usually in the contra-lateral limbs, 90 per cent. The changes in the visual fields found in the majority of cases occurred only in the contralateral halves of the fields. In individual cases the visual fields showed : (a) complete hemianopia up to the fixation point; (b) incomplete hemianopia with spacing of the field for central vision ; (c) quadrantic defects; (d) peripheral crescentic defects-; and (e) no abnormal changes. When vision was failing a concentric contraction of the visual fields was sometimes found added to the above variations. An attempt was made to group the symptoms and physical signs as focal, neighbourhood and those due to increased intracranial pressure. Focal symptoms and signs were limited to unformed visual hallucinations and distortions of the visual fields. Neighbourhood symptoms and signs were of considerable importance in localization, and with the exception of disturbances of speech were probably the result of oedema or vascular changes in the neighbourhood of the tumour, or of pressure upon adjacent structures, sometimes increased by raised supratentorial pressure. Symptoms and signs resulting from increased pressure in some cases were confusing and increased the risk of an error in localization. In the majority of cases symptoms of increased intracranial pressure dominated the clinical picture from the beginning ; in a few epileptiform attacks occurred for some time ; and in others there was a history of exacerbations of increased intracranial pressure for as long as two years.