Objective: Two-alternative forced-choice tasks are widely used to gain insight into specific areas of enhancement or impairment in individuals with autism spectrum disorder (ASD). Data arising from these tasks have been used to support myriad theories regarding the integrity, or otherwise, of particular brain areas or cognitive processes in ASD. The drift diffusion model (DDM) provides an account of the underlying processes which give rise to accuracy and reaction time (RT) distributions, and parameterizes these processes in terms which have direct psychological interpretation. Importantly, the DDM provides further insight into the origin of potential group differences in task performance. Here, for the first time, we used the DDM to investigate perceptual decision making in ASD. Method: Adults with (N = 25) and without ASD (N = 32) performed an orientation discrimination task. A drift diffusion model was applied to the full RT distributions. Results: Participants with ASD responded more slowly than controls, the groups did not differ in accuracy. Modeled parameters indicated that: (a) participants with ASD were more cautious than controls (wider boundary separation); (b) nondecision time was increased in ASD; and (c) the quality of evidence extracted from the stimulus (drift rate) did not vary between groups. Conclusions: Taking the behavioral data in isolation would suggest reduced perceptual sensitivity in ASD. However, DDM results indicated that despite response slowing, there was no evidence of differential perceptual sensitivity between participants with and without ASD. Future use of the DDM in investigations of perception and cognition in ASD is highly recommended.