Purpose The aim of this study was to compare clinical and arthrometrical results of a series of patients older than 40 years with those of younger patients following anterior cruciate ligament (ACL) reconstruction. The hypothesis of this study was that certain biological and biomechanical factors related to middle-aged patients, ACL reconstruction would provide different results compared with younger patients. Methods Thirty-six patients >40 years operated for ACL reconstruction between 2002 and 2010 were selected for this retrospective study, and results were compared with patients in two other age groups (<30 years and 30-40 years). At a minimum follow-up of two years, patients were reviewed and clinically examined subjectively and objectively according to Tegner, International Knee Documentation Committee (IKDC) classification and Lysholm evaluation scales. An arthrometric evaluation with KT-1000 was also performed. Results No statistically significant difference was found among the three different age groups at the subjective and objective evaluations. However, the KT-1000 arthrometric study showed a statistically significant mean side-to-side difference at 30 lb with 1.8 mm [standard deviation (SD) 2.4] for patients >40 years, 2.7 mm (SD 1.8) for patients aged 30-40 years and 2.6 mm (SD 1.8) for patients <30 years. Conclusions Our results seem to show that ACL reconstruction is a safe and valid option for patients of all age groups, even for those >40 years. Moreover, in that group, greater knee stability was found when compared with the younger patient groups.