Objective: The present study investigated whether autistic adults report different levels of mental imagery vividness than non-autistic adults, and, moreover, if autism is associated with aphantasia which is defined as a condition of reduced or absent voluntary imagery. Design and Methods: Clinically diagnosed and self-identifying autistic participants were compared with non-autistic participants in their mental imagery vividness (vision, sound, smell, taste, touch, bodily sensation and emotional feeling) and autistic traits using an online survey (N = 121). Results: The autistic group scored significantly lower than the non-autistic group on imagery vividness (d = -0.44), in addition to having a higher proportion of participants scoring at cut-off for aphantasia. Moreover, a similar difference was observed for the emotional feel (η2 = .11). Conclusion: The vividness of visual and emotional mental imagery was on average lower for autistic individuals, with a higher proportion presenting at cut-off to be considered an aphantasic.