There is debate in the literature regarding the impact of full-thickness cartilage lesion on knee function in patients with ACL injury. The hypothesis of the current study is that a full-thickness cartilage lesion at the time of ACL reconstruction does not influence knee function as measured by the Knee injury and Osteoarthritis Outcome Score (KOOS) in patients with ACL injury. Of the 4,849 primary ACL surgery cases in the Norwegian National Knee Ligament Registry as of 12 December 2007, 30 patients met the following inclusion criteria: a full-thickness cartilage lesion (International Cartilage Repair Society [ICRS] grades 3 and 4), age less than 40 years, no associated pathology or meniscus injury, and less than 1 year between knee injury and ACL reconstruction. Each of the 30 patients in this study group was matched with two control participants without cartilage lesions. Preoperatively, the patients completed the KOOS, and the surgeon recorded the location and size of the cartilage lesion and graded the cartilage injury according to ICRS standards. There were no significant differences between the case and control groups for any of the five subscales of the KOOS. A cartilage lesion was located in the medial compartment in 67% of the cases, in the lateral compartment in 20% of the cases, and in the patellofemoral joint in 13% of the cases. In conclusion, the combination of a full-thickness cartilage lesion and an ACL rupture did not result in inferior knee function at the time of the ACL reconstruction as measured by the KOOS.