The Modified Checklist for Autism in Toddlers (M-CHAT) is a 23-item questionnaire used in primary screening of Autism Spectrum Disorder (ASD). The current studies examine the concurrent validity of the M-CHAT in its ability to predict 18-month-olds' performance on theory of mind and word learning tasks. In Experiment 1, infants' understanding of desires was tested using a modified food request task. Experiment 2 assessed infants' ability to learn novel words. Results indicate that infants' score on the M-CHAT significantly predicts their performance on both the desire understanding and the novel word learning task. As expected, the number of items endorsed on the M-CHAT also relates to infants' expressive vocabulary at 18 months of age. Taken together, these findings confirm the concurrent validity of the M-CHAT at the youngest age this measure can reliably be administered. Within a broader clinical context, the present results provide preliminary evidence that controlled laboratory tasks assessing early social cognitive and verbal abilities could be added to the battery of screening instruments for ASD.