In the tradition of acceptance and commitment therapy (ACT), cognitive fusion is a transdiagnostic risk factor and occurs when one becomes overly attached to or "caught up" in their thoughts, leading to a more narrowed behavioral repertoire and difficulty taking effective action in response to life's demands. Cognitive defusion is ACT's curative answer to fusion, and denotes the process of taking a step back, seeing thoughts as "simply thoughts," thereby reducing the negative impact of distressing or anxiety-provoking thoughts. While these components have been widely studied in neurotypical (NT) samples, the purpose of this study was to extend findings to people diagnosed on the autism spectrum (AS). Specifically, this study aimed to examine the impact of cognitive fusion in this population and the effectiveness of a brief defusion technique. Forty-two AS participants and fifty-five neurotypical participants were given a battery of questionnaires measuring psychological distress and dispositional levels of cognitive fusion. Participants were then randomized into either a brief cognitive fusion technique or a brief active distraction technique. In both conditions participants chose a distressing thought and rated it on a visual analogue scale (VAS) in terms of thought discomfort and believability. They were then read a rationale regarding their assigned technique, practiced the technique, and applied the technique to their chosen distressing thought. After the intervention participants immediately re-rated the thought on the same VAS. Throughout the study, participants' heart rate and skin conductance were monitored to determine physiological effects of the conditions. Finally, a follow-up survey was sent at a one-week and two-week follow-up, where participants re-rated the believability and discomfort of their thoughts. Results of this study showed that the AS group had higher overall levels of fusion than the NT group, and that fusion was moderately to strongly related to psychological distress in the AS group and the NT group. In terms of the intervention effects, all interpretation statements must be taken with caution, as there were significant pre-group differences despite randomization. Both defusion and distraction worked equally well in immediately reducing thought believability and thought discomfort for AS and NT groups. Furthermore, treatment effects were maintained at the two-week follow-up period for all groups except for the AS group in the defusion condition. There were no treatment effects for physiology. The current study provides evidence that cognitive fusion may be an important factor in the psychiatric comorbidity that people with AS experience, and a brief technique can be effectively used.