Abstract
OBJECTIVE: This study aimed to provide a reliable estimate of early childhood autism spectrum disorder (ASD) prevalence in Türkiye and to examine diagnostic stability and developmental trajectories through a ten-year longitudinal follow-up incorporating systematic early screening, structured parent-child observations, and repeated diagnostic assessments. METHODS: A total of 1981 children aged 18-48 months were screened using the M-CHAT-R/F. Children who screened positive underwent an initial clinical assessment, including a family interview and structured parent-child observation. Those identified as at risk were referred for DSM-5-TR-based diagnostic evaluation by expert clinicians. Children diagnosed with ASD or classified as at risk were enrolled in a structured ten-year follow-up program. RESULTS: Of the 1981 screened children, 27 (1.4%) were identified as at risk. Nine children (33.3% of at-risk; 0.45% of the total sample) received an ASD diagnosis following comprehensive evaluation. All retained their diagnosis during the 18-month follow-up. By the tenth year, two additional children from the at-risk group were diagnosed, bringing the total number of ASD cases to 11. CONCLUSIONS: These findings demonstrate that structured, multi-stage screening and diagnostic procedures are feasible and effective for early ASD identification in Türkiye. High diagnostic stability supports the reliability of early clinician-led assessments, while later-emerging cases highlight the importance of long-term monitoring of at-risk children.