Between 1979 and 1989, 105 supracondylar extension osteotomies of the femur were performed to correct knee flexion contractures. Disturbed by serious neurovascular complications, we reviewed our experience. Besides other complications, nine patients developed serious neurovascular complications; seven had permanent residua. There was no correlation between neurovascular complications and degree of preoperative contracture, patients' ages, or scarring from previous operation. We conclude that this osteotomy, although it appears to be technically simple, is potentially dangerous. We propose that the osteotomy be internally fixed and that the knee be flexed to relax the posterior neurovascular structures.