A seminar on 5-Year Olds' Index hosted by the Japancleft Committee, Japanese Cleft Palate Association took place at the Sanjo Conference Hall, the University of Tokyo on July18-19, 2012. The purpose of the seminar was to provide the opportunity to have an exercise in assessing dental arch relation in patients aged 5 years with unilateral cleft lip and palate. Dr. Nikki Atack and Prof. Jonathan Sandy who had developed the index were invited from the University of Bristol as the lecturers at the seminar. The number of participants was over 80 from various special fields such as plastic surgery, oral surgery, pediatric dentistry and orthodontics. A total of 355 dental models were collected from participating institutions and were employed for evaluation training. As a result of intra-examiner agreement and agreement with Gold standard, almost all delegates obtained an agreement score of 0.80 or above, which would be very suitable and able to assess 5 year olds' models. Although the models collected were not selected based upon critical inclusion criteria, the result of assessment of the Japanese models was very analogous to that of UK Pre-CSAG (Clinical Standard Advisory Group). We hope that the present seminar would be helpful for the improvement of treatment outcomes in patients with cleft lip and palate.