The relationship between age at meniscectomy and the time to developing OA requiring an operation was studied. A total of 63 patients (7.8% of those presenting for an operation for OA) had had a previous meniscectomy. It was found that there was a strong correlation between the age at meniscectomy and the time delay (r = -0.68, P < 0.0001). The equation for the regression line was y = -0.68x + 41.8, where y = the delay in years between meniscectomy and operation for OA, and x = the age at meniscectomy. It was noted that there were two distinct populations, those < or = 35 yr old with a mean delay of 26 yr (95% CI 20.8-31.4), and those > 35 yr old with a mean delay of 9.8 yr (95% CI 7.5-12.2). The development of OA requiring an operation following meniscectomy depends on the age at meniscectomy and the time delay. To show an increase rate of OA following meniscectomy in a young population would require follow-up of at least 26 yr.