Everyday conditional reasoning is typically influenced by prior knowledge and belief in the form of specific exceptions known as counterexamples. This study explored whether adolescents with autism spectrum disorder (ASD; N = 26) were less influenced by background knowledge than typically developing adolescents (N = 38) when engaged in conditional reasoning. Participants were presented with pretested valid and invalid conditional inferences with varying available counterexamples. The group with ASD showed significantly less influence of prior knowledge on valid inferences (p = .01) and invalid inferences (p = .01) compared with the typical group. In a secondary probability judgment task, no significant group differences were found in probabilistic judgments of the believability of the premises. Further experiments found that results could not be explained by differences between the groups in the ability to generate counterexamples or any tendency among adolescents with ASD to exhibit a "yes" response pattern. It was concluded that adolescents with ASD tend not to spontaneously contextualize presented material when engaged in everyday reasoning. These findings are discussed with reference to weak central coherence theory and the conditional reasoning literature.