Hereditary optic neuropathies are a prominent cause of blindness in both children and adults. The disorders in this group share many overlapping clinical characteristics, including morphological changes that occur at the optic nerve head. Accurate and prompt clinical diagnosis, supplemented with imaging when indicated, is essential for optimum management of the relevant optic neuropathy and appropriate counseling of the patient on its natural history. Patient history, visual field assessment, optic disc findings and imaging are the cornerstones of a correct diagnosis. This Review highlights the characteristic optic nerve head features that are common to the various hereditary optic neuropathies, and describes the features that enable the conditions to be differentiated.