Anteromedial knee injury with rupture of anterior cruciate ligament (ACL) and concomitant lesion of medial collateral ligament (MCL) is common in athletes. No standardized treatment concept can be found within the literature. This study presents results of a new treatment concept for concomitant MCL lesions in patients with ACL rupture. In this study, 67 recreational athletes with ACL injury and concomitant MCL lesion were treated according to a distinct treatment concept. Patients were classified in six different types of concomitant MCL lesion depending on grade of MCL lesion and presence of anteromedial rotatory instability (AMRI). Final classification and surgical indication were determined 6 weeks posttraumatic. All patients received ACL reconstruction. MCL was treated by surgical or conservative regime due to type of concomitant MCL lesion. International Knee Documentation Committee (IKDC), AMRI, and Lysholm scores were evaluated both preoperatively and after 6 weeks, 16 weeks, 12 months, and 18 months postoperatively. All patients could be uniquely classified and treated according to the introduced treatment concept. AMRI was verifiable in patients with grade II and III MCL lesions. All patients showed good to excellent clinical results at the follow-up examinations. In all 67 patients (100%), the findings were graded as normal or nearly normal according to the IKDC knee examination form. Lysholm score averaged 93.9 at final follow-up. The introduced treatment concept showed good results on short-term outcome and provides a sufficient treatment strategy for concomitant MCL lesions in athletes with ACL rupture.