During four academic years (1974-1978) at a major university, 51 of 70 knee injuries sustained by football players were Grade I or II sprains of the medial collateral ligament of the knee. All were managed identically with an active rehabilitation program involving partial or no immobilization. Players with Grade I sprains returned to full, unprotected participation after an average of 10.6 days of time loss; those with Grade II sprains returned after 19.5 days. Neither group showed an appreciably increased likelihood of reinjury. The likelihood of sustaining any knee injury was more than three times greater during spring as opposed to fall football.