Background: The last decade has seen a vast increase in the use of patient-reported outcomes. As patient-reported outcomes are used in order to capture patients’ perspectives of their health and illness, it is a prerequisite for accurate patient-reported outcome evaluations to use representative samples. In order to evaluate representativeness, the present study focussed on the comparison between participants and non-participants in the Swedish branch of the international study APPROACH-IS (Assessment of Patterns of Patient-Reported Outcomes in Adults with Congenital Heart disease – International Study), regarding demographic, clinical, and health status characteristics. Methods: Eligible patients for APPROACH-IS were identified and selected from SWEDCON, the Swedish registry for congenital heart disease (CHD). Overall, 912 eligible patients were identified, of whom 471 participated, 398 did not participate, and 43 were either unreachable or declined to participate in APPROACH-IS. The participants and non-participants were compared in terms of statistical significance and effect sizes. Results: Significant differences were observed between participants and non-participants for sex, age, primary diagnosis, number of cardiac operations, and fatigue; however, the effect sizes were in general small, except for the difference in primary diagnosis. No differences between the two groups were found in number of catheterisations, implanted device, the distribution of NYHA functional class, or health status and symptoms. Conclusions: This study shows that participants and non-participants are relatively comparable groups, which confirms the representativeness of the participants. The Swedish data from APPROACH-IS can therefore be reliably generalised to the population of adults with CHD in Sweden. © Cambridge University Press 2016