Background: Most adolescent and young adult (AYA) cancer survivors are insufficiently active. Given that AYA cancer survivors' report renewed dependence on their parents, the support (or lack thereof) provided by parents for physical activity (PA) may be a key determinant of PA in this population. As a first step toward understanding and explaining how parents influence their child's PA post-diagnosis, we conducted a qualitative study to explore and contrast AYA cancer survivors' perceptions of the support they receive for PA with their parents' own perceptions of the support they provide. Methods: Ten AYA cancer survivors (Mage=17.4±3.5 years; 70% male) and one of their parents (50% fathers) were interviewed separately. Data were thematically analyzed. Results: Survivors' and parents' perspectives provided differing information that was captured within three broad themes: (1) the basics – encouragement, information, and instrumental support; (2) role-modeling – a double-edged sword; and (3) doing it together – age can matter. AYA cancer survivors appreciated receiving basic forms of support but felt it was least helpful; receiving positive role-modeling and companionship support would have been most helpful. Conversely, parents believed providing basic forms of support would be most helpful and did not recognize that they were important role models. Further, parents hesitated to show interest in participating in PA with their child to prevent behavioural reactance. Conclusion: Our study helps to illustrate that there is a lack of correspondence between AYA cancer survivors and their parents' perceptions of support, and that this may affect AYA cancer survivors' participation in PA.