Little is known about the internal mental experiences of individuals with ASD. While some research suggests a limited capacity for imagination, other studies show heightened interest in fantasy and unique forms of creative thinking in ASD. This study explored daydreaming experiences in adults with ASD, with a focus on immersive daydreaming and its relation to divergent thinking abilities. Individuals with and without a diagnosis of ASD were surveyed on their daydreaming habits and completed a divergent thinking task. Experiences of immersive daydreaming were identified in 42% of adults with ASD and were related to broad ASD traits in those without a diagnosis of ASD. However, ASD diagnosis was unrelated to originality of divergent thinking, which was negatively associated with immersive daydreaming. Moreover, daydreaming experiences in ASD were diverse. A more nuanced understanding of the mental experiences in ASD may assist in the development of interventions and support for this population.