We assessed the outcome after simultaneous multiple operations performed on 18 children with spastic diplegia, with emphasis on the changes in the physiological cost index (PCI) of walking. Fourteen patients had a measurable reduction at one year, but the more severely affected patients took up to two years to reach a new functional plateau. The level of the preoperative PCI allows prediction of the outcome of surgery in terms of reducing the effort of walking, or improving its appearance only. Intrapelvic intramuscular psoas tenotomy produced an improvement of hip flexion deformity in 15 of 17 patients without the loss of muscle power to initiate the swing phase. Fractional lengthening corrected hamstring tightness in 17 cases, and the mean popliteal angle was reduced from 63 degrees preoperatively to 30.2 degrees, with almost complete resolution of the fixed knee flexion deformity present in ten patients. Distal transfer of the rectus femoris, when it was shown to be contracting inappropriately, improved the knee flexion arc during walking from a mean of 28.3 degrees to 45.2 degrees.