The prevalence of autism has increased dramatically over the past 10 years, however, reported measures of prevalence do not accurately assess the role of the environment over better diagnostic techniques and service availability. This is better evaluated by measuring the incidence of autism over time – that is, the number of new cases initially not diagnosed with autism, then later diagnosed with autism on a yearly basis using rigorous screening, standard diagnostic assessments and valid case ascertainment in a specific age category over successive years. In addition, the study must include a defined group and accurately assess all members of that group. Because Korea is a relatively genetic homogeneous group as compared with other countries, and because the investigators have established the parameters listed above in their previous studies investigating autism in a geographically defined region in a large group of people, this is an ideal situation to examine the changes in incidence and prevalence over time. The investigators in Korea and in the US have already developed methods to identify, screen and diagnose children with autism using a grant from Autism Speaks in 2005. Therefore, this project will allow Dr. Kim and her colleagues to analyze incidence rates over time in 6 year olds with autism in Korea.