Background: International guidelines recommend planned and structured transition programmes for adolescents with chronic illness because inadequate transition may lead to poor disease control and risk of lacking outpatient follow-up. Objective: To investigate the feasibility of a transition intervention aimed at adolescents with chronic illness focusing on declines, drop-outs, no-shows and advantages and disadvantages of participating. Methods: We invited 236 adolescents (12-20 years) with juvenile idiopathic arthritis (JIA) to participate in a randomised controlled trial (RCT) transition intervention. Reasons for decline and drop-outs were calculated. Adolescents' experiences of advantages and disadvantages of participating and reasons for no-shows were investigated through focus groups and telephone interviews, which were analysed using thematic analysis. Results: One hundred and twenty of the 236 eligible patients declined to participate in the intervention and 20% dropped out during the intervention. Unspecified declines and practical issues were the most common reason to decline, and 'do not wish to continue' was the most common reason to drop-out. Reasons for no-shows were forgetting and being too busy. Advantages of participating were stated as 'participating without parents', 'trust and confidentiality', 'being able to set the agenda' and 'responsiveness'. Disadvantages were 'unclear aim of the study', 'meeting others with JIA', 'too few conversations' and 'transport issues'. Conclusions: Many adolescents had difficulties understanding the aim of the intervention. However, most participants appreciated the conversations about identity as well as the trust and confidentiality in the communication. In the future, adolescents should be offered more individually organised programmes according to their preferences and needs in cooperation with parents and health care providers.