As many children and infants with developmental delay have been screened every year, clinicians have to focus on evaluation of delayed development children. Furthermore increasing evidences indicate early intervention can be helpful to the children with Autism Spectrum Disorder (ASD). The aim of this study is longitudinal overview of children and infants with delayed development who visit our clinic. 733 children visited out clinic from March 2010 to August 2014. Out of these 744 patients, 126 patients who visited our clinic more than twice were enrolled. All patients visit three departments ( Pediatric neurology, Rehabilitation, Psychology) under principle of multi-disciplinary approach. PRES, SELSI tests were performed for speech evaluation. Bayley scale, K-WPPSI, K-WISC for cognition, SMS, CBCL, K-ABC for social and emotional evaluation were done. Brain MRI, chromosome or genetic screening were done on neurologist’ s request. The mean age at 1st visit was 2.6 years and 2nd visit was 4.8 years. Mean follow up interval between 1st and 2nd visit was 25.5 months. Of total 126 children, 80 children were boys and 46 children were girls. Most common chief complain of visited children was language delay (73.3%). Global delay (15.8%), motor or social developmental delay (10.3%) followed. Among them 16.6% patients were referred from screening program. At 1st visit, 29.9% of patients were diagnosed as developmental language delay (DLD), 26.5% as global developmental delay (GDD). After follow up, 50.5% of children revealed MR, 28.8% were diagnosed as ASD. Almost patients who diagnosed as ASD and MR were not changed after follow up. But, children diagnosed as GDD at 1st visit were changed their diagnosis to MR (62.5%), ASD (25%) at 2nd visit. And children with DLD at 1st visit were changed to MR (68.7%), ASD (31.2%). Among children with 1st diagnosis was GDD, children with preserved cognitive functions than motor function (MDI/PDI＞1) showed tendency of better prognosis. and in DLD patients Bayley scale were higher in better prognosis patients than MR and ASD patients. ASD patients whose 1st diagnosis was DLD showed relative higher PDI than MR patients. Follow up is most important part because large number of DLD and GDD patients finally diagnosed as MR and ASD. Although preliminary data, we found out discriminative characters in better prognosis children.