In this international study, we (1) compared patient-reported outcomes (PROs) in adults with congenital heart disease (CHD) who had versus had not been hospitalized during the previous 12 month, (2) contrasted PROs in patients who had been hospitalized for cardiac surgery versus nonsurgical reasons, (3) assessed the magnitude of differences between the groups (i.e., effect sizes), and (4) explored differential effect sizes between countries. APPROACH-IS was a cross-sectional, observational study that enrolled 4,028 patients from 15 countries (median age 32 years; 53% females). Self-report questionnaires were administered to measure PROs: health status; anxiety and depression; and quality of life. Overall, 668 patients (17%) had been hospitalized in the previous 12 months. These patients reported poorer outcomes on all PROs, with the exception of anxiety. Patients who underwent cardiac surgery demonstrated a better quality of life compared with those who were hospitalized for nonsurgical reasons. For significant differences, the effect sizes were small, whereas they were negligible in nonsignificant comparisons. Substantial intercountry differences were observed. For various PROs, moderate to large effect sizes were found comparing different countries. In conclusion, adults with CHD who had undergone hospitalization in the previous year had poorer PROs than those who were medically stable. Researchers ought to account for the timing of recruitment when conducting PRO research as hospitalization can impact results.