We have treated two cases of rupture of ligamentum patellae with avulsion fracture of the patella.Case 1: On May 29, 1985, an 11-year-old boy suddenly fell to the ground while roller skating. Subsequently he was unable to walk.On May 33, 1985, he was admitted to our hospital.Examination revealed left swollen knee with patella alta and loss of tension of ligamentum patellae. Roentgenogram revealed patella alta and a small bony fragment shadow. A diagnosis of rupture of ligamentum patellae was made.On June 4, 1985, operation was performed. At the operation, ligamentum patellae was ruptured with avulsion fracture of the patella. Fragment was excised and end to end suture was performed.Postoperatively plaster cast was applied and two weeks after operation he was allowed crutch gait with cylinder cast. Six weeks after operation cast was removedSix months after operation he had no complaints in his left kee joint.Case 2: On October 14, 1985, 11-year-old boy had severe right knee joint pain at the time of high jump. Subsequently, he was unable to walk.On October 18, 1985, he was admitted to our hospital.Physical examination and roentgenogram revealded rupture of ligamentum patelle with avulsion fracture of the patella.On October 22, 1985, operation was performed by the same procedure as the former case and postoperative treatment was done by the same schedule.Six months after operation he had no complaints in his right knee joint.