Significant traumatic disruption of the ligaments about the knee can occur in a child. Recently several reports have described knee ligament, injuries with open growth plates. And these reports contradict the notion that complete tears of knee ligaments occur only after growth plates have closed. The youngest patient with medial collateral ligament injury reported before was a 4-year-old boy by Joseph and Pogrund in 1978. But authors experienced a case of ruptured medial collateral ligament of the knee in a 2-year and 1-month old boy, who seemed to be youngest with the ligament injury.