A followup study was performed to elucidate the natural course of acutely torn anterior cruciate ligaments in recreational athletes. Fifty-six consecutive patients had arthroscopy within 2 weeks of their initial injuries; however, no surgery was done on the torn anterior cruciate ligament. Twenty anterior cruciate ligament and medial collateral ligament combined ruptures occurred. Patient ages ranged from 14 to 50 years old (mean, 28.9 years). Followup periods ranged from 2 to 10 years (mean, 5 years 6 months). Through examination with the KT-1000 arthrometer, side-to-side differences of anterior translation of the tibia of > or = 3 mm in 72% patients at reexamination were seen. Eight of 46 patients had mild osteoarthritic changes of Grade 1 visible on radiographs, but only 1 patient reported knee trouble. Nine patients had repeat injuries, 3 of whom had late reconstructions and 4 late meniscectomies. Functional scores averaged 95 +/- 6.5 points. Activity scores averaged 4.8 +/- 1.6 points. Operative management for the medial structure did not improve the stability better than nonoperative management. Anterior translation and functional scores of patients with medial meniscectomies showed significant differences from those of other patients. Anterior cruciate ligament reconstruction for recreational athletes should be considered when the patients have reparable meniscal tears, and meniscal repairs should be performed simultaneously.