Background: Adolescents and young adults (AYAs) with cancer have poor psychosocial outcomes, in part because their limited participation in clinical trials precludes intervention-testing. We previously reported results of a successful randomized trial testing an AYA-targeted psychosocial intervention. Here, we aimed to describe strategies learned during the trial’s conduct. Methods: We summarized data from the medical record and staff field notes regarding reasons for participation/non-participation. We conducted two focus groups with study staff; directed content analyses identified strategies for success. Results: 92 AYAs enrolled (77% of approached; n = 50 Usual Care (control), n = 49 PRISM (intervention)). In eligible families who declined participation (n = 22 AYAs, n = 8 parents), the AYAs more commonly had advanced cancer (n = 11 (37%) declined vs. n = 25 (26%) enrolled). AYA reasons for non-enrollment were predominantly “not interested”; parents worried participation was “too burdensome.” Staff strategies for accrual included having significant time to introduce the study and underscoring a desire to learn from the patient. After enrollment, AYAs who discontinued participation were more commonly assigned to control (n = 5 (10%) control vs. n = 2 (4%) intervention). Only n = 1 AYA chose to discontinue participation after receiving the intervention. Conclusions: Efforts to engage AYAs prior to and during studies may help with accrual and retention.