Arthrodesis of the metacarpophalangeal joint of the thumb is a well-accepted procedure. Recommendations for position of fusion have varied from 0 to 30 degrees of flexion. Two hundred of these joints in normal subjects were measured in thirteen positions of function for different tasks. The mean of all thirteen measured positions was considered to be the "optimal functional position". Based on this study, we recommend the metacarpophalangeal joint of males be fused in approximately 25 degrees of flexion and females in 20 degrees of flexion.