The lateral substitution reconstruction operation described by MacIntosh has been evaluated in 27 patients with chronic anterior cruciate ligament deficiency of the knee. The results, at an average of 11.3 years after operation, have been assessed by a scoring system which allocates a maximum of 25 points each for function and for clinical evaluation. Emphasis was placed on subjective giving way and objective evidence of a positive anterior drawer sign and a positive lateral pivot shift test. A score of 46 to 50 was classified as excellent, 41 to 46 as fair, and less than 41 was a poor result: 52% scored excellent, 26% fair and 22% were poor. Most of those with poor results had had evidence of osteoarthritis at the time of operation. Despite the recorded scores, no less than 75% of the patients at long-term follow-up were subjectively improved, and able to maintain an active life style.