An extreme case of slipping patella was observed in the Children's Hospital, in a girl aged about 9 years, with a double congenital dislocation of the patella gradually increasing in laxity. The ordinary methods of treatment did not seem appropriate or adequate. The left patella constantly and without warning would dislocate over the external condyle, causing the child to fall without warning. The action of the quadriceps was uncertain, and walking was not sure. The child was healthy and normal. Examination of the legs showed good muscle tone and normal range of motion of the hips, knees and feet. Everything was normal except for the knees. One was impressed with four things: (1) the looseness of the patellar ligament and all the tissues to the inner side of the patella; (2)the ease with which the patella could be placed over to the outer side, so far over that the internal