Seventeen patients thought to have orbital optic nerve gliomas when first seen have been reviewed after up to 12 years. Enlargement of the optic canal was present in 15 of the 16 patients examined, but this finding was unreliable as an indicator of the posterior extent of the tumour. Nine patients had a stable course with little change over a period of up to 8 years; there was optic atrophy in all and neurofibromatosis was relatively common (7/9). Eight patients showed progressive enlargement of the tumour; 6 had swollen discs, and the incidence of neurofibromatosis was relatively low (3/8). The optic nerve was excised in 7 of the latter group. Biopsies of the optic nerve taken from the region of maximal enlargement were difficult to interpret and unhelpful in planning management. Radical surgery should be reserved for the minority of patients in whom there is progressively enlarging tumour without evidence of chiasmal involvement.