Anterior cruciate ligament (ACL) insufficiency is unusual in children younger than 14 years of age. Nontraumatic ACL laxity is found in two distinct groups of children: (1) those with generalized nonpathologic joint laxity, and (2) those with congenital absence or attenuation of the ligament, usually associated with other congenital anomalies in the same limb. ACL insufficiency secondary to trauma most often is associated with avulsion of the intercondylar eminence of the tibia. Excellent results have been obtained following anatomic reduction by either closed or open methods. In children, insubstance damage to the ACL, alone or associated with other ligamentous injuries, is distinctly unusual. In three patients younger than 14 years of age with midsubstance tears of the ACL, no other clinically evident ligamentous injury was noted. All three were treated by primary surgical repair without intra- or extra-articular augmentation procedures. Despite only mild subjective complaints at follow-up examinations, all three patients had at least moderate degrees of clinical ACL laxity, suggesting that midsubstance ACL injuries in children have no better healing potential than in adults.