The treatment of acutely torn anterior cruciate ligament(A.C.L) remains a controversial subject. The purpose of this paper is to show the arthroscopic technique of A.C.L. primary repair with or without augmentation with semitendinosus tendon. Twenty-one patients with acute A.C.L. tear were treated with repair or augmented repair under arthroscopic control from April 1989 to August 1993. Five A.C.L. torn at femoral attachment with intact distal stump were treated with arthoscopic repair alone & 16 A.C.L. torn at substance near the femoral attachment with arthroscopic repair & augmentation with semitendinosus tendon. The patient population included of 16 males and 5 females with an average age 28.3 years. Fifteen patients injuried during sports activity. Postoperative results were evaluated by Lysholm knee score & Hospital for Special Surgery knee scale in average 26 months (range from 12 months to 64 months). All patients were rated as good or excellent result except one patient who had fair result. At follow-up study, testing with KT₁₀₀₀ arthrometer revealed 17 patients had less than 3mm of side to side difference. Second look arthroscopy was performed in 15 patients from 4 to 29 months after repair or augmented repair. Eleven out of these 15 A.C.L. were well healed with good tension 8r. revascularization of graft. Remaining 4 A.C.L. were healed with scar tissue. On the based of this study, arthroscopic repair or augmented repair is very effective treatment for acutely torn A.C.L. near the femoral attachment.