This syndrome was described by Rubinstein and Taybi in 1963. As yet seventy five cases were reported in Japan, but there are few reports described on the dental findings. The oral findings and its treatment were reported in this study. The clinical characteristic features of the Rubinstein-Taybi syndrome were almost observed in this case. Especially, according to the oral findings, the highly arched palate, undergrowth of the both jaw, the remarkable crowded teeth and intense marginal gingivitis showed in this case. Further, this case showed the characteristic features as upper supernumerary incisors, anterior and posterior cross bite and missing of upper right premolar. But in this case, the malformed tooth and imperfect tooth were not presented. The care for the mental retardation and the constant acute respiratory disease are nessesary in treatment with the syndrome.

We made a plan of the treatment as follows,

1)Extraction of ectopic teeth in order to prevent from gingivitis due to markedly crowded teeth and multiple caries.

2)Conservation treatment of caries.

3)Tooth-brushing instruction for gingivitis.

4)Expansion of maxilla for cross bite.

The above plan is almost successful.