Abstract Aims To assess tumour control, visual outcomes and toxicity after radiotherapy for all patients with optic nerve sheath meningiomas (ONSM) treated by a single radiation oncologist at a single institution over a 15 year period. To explore potential predictors of outcomes. Materials and methods All patients underwent ophthalmological and radiological assessments before radiotherapy. These were repeated at regular intervals after treatment. A retrospective analysis of clinical, dosimetric and radiological data was carried out. Patients with useful vision before radiotherapy were divided into two groups – those with maintained or improved vision and those with a deterioration in vision. The groups were compared using the Mann–Whitney U-test with regard to eight potential predictors of outcome. Results Seventeen patients with 18 ONSM were treated with fractionated radiotherapy (46.8–55.8 Gy in 26–31 fractions). No evaluable tumours grew after treatment: control rate 100% (95% confidence interval 82–100%). Using the most common definition of visual function described in the literature, vision was maintained or improved in 89% (95% confidence interval 67–97%) of cases. In those with useful vision before treatment (13 evaluable eyes), visual acuity was maintained or improved in eight (62%, 95% confidence interval 36–82%). There was a suggestion that the time from the onset of symptoms to radiotherapy may influence outcome. Those with stable or better visual acuity after radiotherapy had been observed for a shorter time compared with those who had worse visual acuity (median of 18 months versus 62 months). Acute and late toxicity from radiotherapy was manageable. Conclusion Radiotherapy is an extremely effective modality in arresting the growth of ONSM. A longer time from symptom onset to the start of radiotherapy may predict for poorer outcomes.