Purpose <p>Theory of mind is the capacity to understand others’ mental states, such as their thoughts, beliefs, and feelings, even when they differ from one’s own. The Short Story Task is a measure of individual differences in theory of mind in adults, where respondents are scored on the accuracy of their mental state inferences about characters in the story. However, it collects open-ended responses and thus requires labour-intensive subjective scoring. The present study tested the validity of a new multiple-choice response format of the Short Story Task (SST-MCQ).</p> Method <p>People on the Autism Spectrum can have difficulty with theory of mind. Therefore, a common validation approach for theory of mind measures is to demonstrate reduced task performance for those on the Autism Spectrum and/or those higher in autistic traits. Here, participants with an Autism Spectrum diagnosis and neurotypical participants were recruited for two studies, and participants completed the SST-MCQ and Autism Quotient (AQ-10).</p> Results <p>A combined analysis of the two studies (256 Autism Spectrum participants and 263 neurotypical) showed higher autistic traits as measured by the AQ-10 were associated with lower SST-MCQ scores (<i>r</i>_<i>s</i> = − 0.11). When restricted to those who AQ scores matched their group classification (126 Autism Spectrum and 246 neurotypical), the Autism Spectrum group had lower SST-MCQ scores than neurotypical participants (<i>r</i>_rb = 0.13).</p> Conclusion <p>These findings suggest that SST-MCQ scores provide a valid measure of individual differences in theory of mind ability for adult participants.</p>