The author surveyed the tooth development of 50 cleft affected children(M: 34, F:16). The following results were obtained. 1. The difference between the chronologic age and dental age was 0.61 years in the cleft group and 0.15 years in the control group. The delay in tooth development was observed in the cleft group. 2, In the cleft group, there was no difference in the delay of tooth development between the boys and the girls. 3. In the cleft group, there was no difference in the delay of tooth development between the maxilla and the mandible. 4. The delay of tooth development was more severe in the bilateral cleft group than in the unilateral cleft group. 5. In the unilateral cleft, there was no difference in tooth formation between the cleft side and corresponding side.