One hundred and sixty-five different surgical procedures were performed for the correction of thumb deformities in fifty-six patients with spastic cerebral palsy at Gillette Children's Hospital, St. Paul, Minnesota, between 1967 and 1975. The quality of voluntary muscle control and sensibility were the most important factors in predicting the success of operation. In the past, thumb deformities were classified on the basis of the static position of the thumb, but rational treatment decisions can be made only by a careful assessment of the patient's hand and thumb function. Using various combinations of releases, tendon transfers, and joint stabilizations, measurable and predictable improvement in function was achieved in all fifty-six patients whose records were analyzed.