Background: A novel exercise modality termed Assisted Cycling Therapy (ACT) has been used successfully in patients with Parkinson's disease, but its effects in adolescents with autism spectrum disorder (ASD) have not been investigated. Method: The aim was to examine the acute effects of 2 modes of exercise on cognitive and motor functioning in adolescents with ASD. Participants (N = 10) randomly completed 3 interventions on nonconsecutive days. The interventions were (a) voluntary cycling (VC), in which participants cycled at their self-selected pedalling rate; (b) ACT, in which the participants' voluntary pedalling rates were augmented with a motor to ensure the maintenance of 80 rpm; and (c) no cycling (NC), in which the participants sat and watched a video. Results: Participants' inhibition improved significantly and improvements in cognitive planning and set-switching approached significance after a single session of ACT; however, no improvements in inhibition, cognitive planning, or set-switching were observed following the VC or NC sessions. Exercise perception improved after the VC session but did not change after the ACT or NC sessions. Conclusions: ACT appears to benefit cortical structures in adolescents with ASD, but a chronic intervention may be necessary to improve exercise perception and self-efficacy.