Polydactyly of the thumb is frequently seen among congenital anomalies. Twenty-four hands of 22 patients were operated at our department, and registered in this study. One hand was classified as Wassel's type 1, 5 hands as type 2, 1 hand as type 3, 8 hands as type 4, 3 hands as type 5, 0 hand as type 0, 6 hands as type 7. The age at initial operation ranged from 7 months to 42 months with a mean of 14.0 months. All patients were examined using modified Tada's criteria. The results were good in 19 hands, fair in 5 hands (4 hands of type 4 and 1 hand of type 1). 80% of fair cases were type 4. Eight hands of type 4 were analyzed in order to determine factors affecting the outcome. Fair hands all showed more than a 20 degree radial deviation of the interphalangeal joint (IPJ). Our results suggest that cases of more than 20 degree malalignment at the IPJ initially needs the correction osteotomy of the proximal phalanx.