Delta phalanx is a rare congenital anomaly whose phalanx, metacarpal or metatarsal is triangular or trapezoidal in shape with an abnormal C-shaped physis that causes angular deformity. This diagnosis can be confirmed only radiologically and it can be associated with many other abnormalities of the hand and foot. We report 30 cases of delta phalanges in 23 patients who were surgically treated at Seoul National University Hospital Since 1983. Thirteen were males and 10 females. Nineteen cases occurred at hand and 11 at foot. Thirteen cases were associated with polydactyly. Triphalangeal thumb, syndactyly, oligodactyly and absence of finger were also found to be associated with this anomaly. Twelve were treated by osteotomy, 7 by partial or total excision, 4 by resection arthrodesis, 4 by rotational epiphysioplasty, two by excision and bone transfer and one by shaving. They were followed up at least for 1 years and 2 months and the longest for 6 years and 1 month, on an average of 2 years and 5 months. The criteria for the surgical results were arbitrarily determined as satisfactory when the range of motion of the adjacent joint was more than 20% of the normal, the angular deformity was below 15°and the parents were satisfied. The result was rated as fair when it satisfied either one of the first two criteria, and the parents were pleased with it. Unsatisfactory result means that it satisfied neither of them. According to this criteria, we got 5 satisfactory cases out of 7 by excision, all out of 4 by resection arthrodesis, 3 out of 4 by rotational epiphysioplasty. There were 11 unsatisfactory cases out of 12 by osteotomy and all out of 2 in case of excision and bone transfer. In conclusion, resection arthrodesis or rotational epiphysioplasty would be better choice rather than corrective osteotomy for delta phalanx of the growing children and corrective osteotomy can be an option recommendable after the closure of the physis.