An aspect of metacognition associated with broader functional abilities in several clinical conditions, but previously unexamined in autism, is "self-assessment" (i.e., the ability to accurately self-evaluate one's own performance). We compared self-assessment between 37 autistic adults without intellectual disability to 39 non-autistic (NA) controls on a series of three general cognitive and three social cognitive tasks. Whereas autistic adults and NA adults did not differ in their self-assessment accuracy on general cognitive tasks, they did on social cognitive tasks, with autistic adults demonstrating lower accuracy. The direction of their inaccuracy was variable (i.e., both over and underestimation), and self-assessment was largely unrelated to their level of social functioning. Over versus underestimation may have different functional implications, and warrants future investigation.