The early management of bilateral congenital popliteal webbing in a brother and sister is described. There was no familial history of webbing, but the maternal grandfather had a hare-lip. Although the sciatic nerve is so unfavourably placed in the web, correction of the flexion deformity can apparently be carried out safely after plastic repair of the skin by Z-plasty and excision of the fibrous web cord alone, without causing a traction paralysis. These cases appear to be unique in that the patients are siblings of different sex with identical congenital abnormalities of bilateral webbing, cleft palate and fistulae of the mucous membrane of the lower lip.