We report the results of a prospective longitudinal study of 147 athletes who had had a meniscectomy for an isolated meniscus injury. The patients were reviewed in detail after median periods of 4.5 years and 14.5 years and the results analysed. The frequency of complaints related to the operation increased from 53% at 4.5 years to 67% at 14.5 years, while demonstrable knee instability increased from 10% to 36%. The incidence of radiographic changes of degeneration rose from 40% to 89% and at late review 8% of patients had definite osteoarthritis by the criteria of Ahlback (1968). In consequence 46% had given up or reduced their sporting activity, and 6.5% had changed their occupation. Radiographic deterioration started after the 4.5-year review in 49% of the patients and was more frequent after lateral than medial meniscectomy.