The purposes of this study were to evaluate the diagnostic modalities of the acute rupture of anterior cruciate ligament(ACL) and to know the differences hetween complete and partial ACL rupture preoperatively, analyzing the methods of physical examimation and the clinical features in acutely injured patient. We analyzed the anterior drawer test, Lachman test, KT-2000 arthrometer, MRI findings and associated injuries in the 35 patients who were confirmed to have ACL rupture by arthroscopy of the knee joint, performed within a month after trauma. We divided the patients by arthroscopy into 2 groups: complete rupture group and the partial rupture group. Among the 35 cases of ACL rupture, there were 10 cases of partial rupture and 25 cases of complete rupture. The Lachman s test was the most sensitive method of the physical examinations in detecting acute ACL injuries, with 90% and 92% positive rate in each group retrospectively. KT-2000 arthrometer with more than 3mm side-to-side difference showed all positive findings except one. The findings of ACL rupture in MRI were discontinuity, increased signal intensity, ahnormal course of ACL fibers and so on. The sensitivity of MRI in diagnosing the acute injuries of ACL was 97.2% hut had difficulties in differentiating the complete from partial rupture. Associated injuries of the ACL injured knee were medial and lateral meniscus tear and medial collateral ligament injury. The diagnosis of acute ACL rupture was made possihle hy physical examinations and with use of the KT-2000 arthrometer and MRI was useful in detecting the ACL rupture or associated injuries but not in differentiating complete from partial rupture of the ACL.