The clinical presentation of 26 knees in 25 children with habitual dislocation of the patella caused by contracture of the quadriceps muscle was studied. They had all received intramuscular injections to the thigh during infancy. The predominant symptom was sudden giving way of the knee during activity. The patella dislocated everytime the knee flexed and when allowed to do so, full flexion was possible; when it was prevented from dislocating, knee flexion was limited in all cases. At operation, it was noted that the contractures were confined to the iliotibial band, vastus lateralis and the lateral fibres of the rectus femoris muscle. Division of the contracted bands corrected the dislocation. In four cases, medial plication was required as an additional procedure. A post-operative extensor lag of the knee was present in all cases, which recovered within one year.