To document the incidence of intra-articular pathology resulting from delayed Anterior Cruciate Ligament (ACL) reconstruction A prospective assessment of meniscal and chondral damage found at the time of primary ACL reconstruction, and the relationship of incidence of intra-articular pathology to time since original ACL injury. We reviewed 1960 patients who had undergone a primary ACL reconstruction. There were 1443 Males and 517 females, with an average age of 28.3 years. The average age at injury was 25.4 years. 1136 patients (58%) had secondary intra-articular pathology, 621 (54.7%) had a medial meniscal tear, 594 (52.4%) had a lateral meniscal tear and 381 (33.5%) had chondral damage. The average time from injury to reconstruction was 2.9 years (34.8 months) Those with secondary intraarticular pathology presented for reconstruction later, average 3.9 years (46.8 months), compared to those without secondary pathology, average 1.5 years (18 months). The incidence of secondary intra-articular pathology increased with delay between original ACL injury and reconstruction. 41% of those waiting 12 months; 60% of those waiting 3 years; 79% of those waiting 5 years and 88% of those waiting 10 years had secondary intra-articular pathology. This study confirms the relationship between an unstable ACL deficient knee and the incidence of secondary intra-articular pathology. Furthermore, our study reveals the increasing incidence of meniscal and chondral pathology the greater the delay from injury to ACL reconstruction. To prevent unnecessary secondary intra-articular pathology we recommend ACL reconstruction is performed with minimal delay.