OBJECTIVE Visual failure due to optic nerve compression is a common indication for decompressive surgery. Most data only refer to the odds of improvement, deterioration or remaining the same. However, patients frequently wish to know more detail about the outcomes of surgery. Our aim was to assess the visual outcome from optic nerve decompression for visual failure in detail in order to help counsel patients pre-operatively. METHODS Sixty-eight patients undergoing 71 operations to decompress 87 optic nerves between 1991 and 2007 were identified. Thirty-four decompressions were performed via a transzygomatic and 37 via a transbasal approach. Fifty-two patients had meningiomas, 3 pituitary adenomas, 3 craniopharyngiomas, 3 chordomas, 2 adenocarcinomas, 2 fibrous dysplasia, 1 schwannoma, 1 granular pituitary tumour and 1 olfactory neuroblastoma. Visual acuity and fields were recorded pre-operatively, immediately post-operatively, at first follow-up and at most recent follow-up. RESULTS Forty-three eyes (49.4%) experienced an improvement in either acuity or fields. Twenty-four (27.5%) were unchanged and 20 (22.9%) deteriorated. Average improvement was 0.88 Snellen lines (logMAR 0.13). Improvement was seen between immediate post-operative acuity and first follow-up in 52%, but 22% suffered a late deterioration after 1 year. There was no relationship between age, duration of symptoms, pathology, approach or redo surgery and visual outcome. There was a complex relationship between pre-operative visual acuity and post-operative improvement and outcome. Better pre-operative acuity predicted better outcome and greater odds of improvement, although patients with poor pre-operative vision had a greater average magnitude of improvement. CONCLUSIONS Patients experience significant benefit from optic nerve decompression irrespective of pre-operative visual status. Although early decompression is desirable, good results can still be obtained in patients with severe visual failure. Detailed data on visual outcome can help counsel patients pre-operatively to aid decision-making and set expectations.