This review of optic nerve and chiasmal disease briefly outlines the clinical assessment and the use of diagnostic testing in the topical diagnosis of lesions of the anterior visual pathways. The commoner pathological entities including inflammatory, vascular, heredofamilial and compressive lesions are then summarised with specific reference to important points in the diagnosis and management. Specific disorders described include optic neuritis, papilloedema, ischaemic optic neuropathy, giant cell arteritis, Leber's hereditary optic neuropathy and pituitary tumours.