The study examined the clinical utility and psychometric properties of the Korean Modified Checklist of Autism in Toddlers (K-M-CHAT)-2. A sample of 2300 parents of 16- to 36-month-old children was recruited across South Korea. A phone interview was utilized to follow up with participants who initially screened positive for autism spectrum disorder (ASD). Item response theory was applied to assess the psychometric properties of the K-M-CHAT-2. Parents’ responses were substantially changed after the follow-up, and the final screen-positive rate was 2.3 %. Results indicated that the psychometric properties of items 1, 3, 11, 18 and 22 were not as strong as the other items. The K-M-CHAT-2 is a useful ASD screening test when implemented with a follow-up.