Two hundred and five patients with ACL rupture, who had been diagnosed pre-operatively by either MRI scan or knee arthroscopy, had reconstructions between 2003 and 2007. The diagnostic meniscal findings were compared with those at reconstruction, and any further damage along with time from diagnosis to reconstruction was recorded. Those patients with no meniscal damage at the time of diagnosis, and who had no further damage at surgery had a median time of 6 months. This time was significantly different from those with no meniscal damage at diagnosis, but who were found subsequently to have sustained damage to one meniscus, when the median time was 11 months (P = 0.0017) or both menisci, when the median time was 32 months (P = 0.0184). For patients with solitary ACL rupture undergoing a trial of conservative management, an early and thorough assessment of functional stability is essential. If the instability is unacceptable, the patient should be informed of the time dependent risk to the menisci with further delay to surgical reconstruction.