For intraoperative injuries of the medial collateral ligament (MCL) during primary total knee arthroplasty (TKA), many authors recommended complex reconstructive procedures or conversion to the constrained prosthesis in previous literature. However, it is well known that medial collateral ligament has good healing potential after injuries. This retrospective study evaluated the clinical and radiological results of 15 primary TKAs complicated with intraoperative complete detachment of the MCL from tibial attachment site, which were all treated solely by nonoperative conservative treatment without any other additive procedures or braces. Compared to the MCL-intact contralateral knees, there was no significant difference in terms of clinical and radiological outcome at minimum of 2 postoperative year. There was no case showing clinical instability, either. Solely, the nonoperative conservative treatment for intraoperative injuries of the MCL during primary TKAs is expected not only to be effective with satisfactory results but also to decrease complications derived from other sophisticated reparative or reconstructive procedures.