The modified checklist for autism in toddlers (M-CHAT) is a tool developed for 16-30 month old children to screen for autism spectrum disorders (ASD). It is a well-researched tool, but little is known about its utility with Singaporean toddlers and with older children referred for developmental concerns. This study investigated the M-CHAT's performance with 18-30 month old (N = 173) and >30-48 month old (N = 407) developmentally at-risk Singaporean children, when used with three recommended scoring methods i.e., the total, critical and Best7 scoring methods. The results indicate that the critical and Best7 scoring methods detected most true cases of ASD without inflating the false positive rates in toddlers, and that only the total scoring method performed acceptably for the older children.