The aim of this study is to assess the need for orthodontic treatment in a Turkish school population and a group of population referred for orthodontic treatment. The study groups were 250 school children, 11-14 years of age, and 250 patients, 11-14 years of age, referred to the department of orthodontics. The Index of Orthodontic Treatment Need (IOTN) was used by two examiner in order to estimate the treatment need. The differences between the IOTN values for the boys and girls were also not statistically significant in both groups. When the dental health component of IOTN is considered, 38.8 per cent of Turkish school population showed great need treatment, 24.0 per cent moderate need treatment and slight or no need was 37.2 per cent. On the other hand, the referred population represented an 83.2 per cent great need treatment, 12.0 per cent moderate need treatment, 4.8 per cent no need treatment according to the DHC. The AC of IOTN in school population resulted in 4.8 per cent great need, 4.8 per cent moderate need, 90.4 per cent no need. These percentage were 36.8 per cent great need, 17.6 per cent moderate need, 45.2 per cent no need in referred population. Grade 8 was 28.8 per cent out of the 36.8 per cent great need percentage in referred population. Therefore, it can be concluded that the ectopic canines were the driving factor for the referred population.