Abstract Background Prior research has demonstrated that a significant proportion of older patients with congenital heart disease (CHD) are frail or pre-frail and experience cognitive impairment. However, it remains unclear whether frailty and cognition are related to patient-reported outcomes (PROs) such as perceived health, anxiety and depression symptoms or quality of life in CHD. Purpose The objective of this study was to explore the relationships between frailty, cognitive function, and PROs in middle-aged and older adults with CHD ranging from mild to severe complexity. Methods As part of the cross-sectional ‘Assessment of Patterns of Patient-Reported Outcomes in Adults with Congenital Heart disease – International Study II’ (APPROACH-IS II), we enrolled 814 individuals aged 40 years and older (median age: 52.0 years [45.0-61.0]; 51.4% female; 12.7% mild, 70.1% moderate, 17.2% complex CHD; 41.9% pre-frail, 5.8% frail; 38.7% cognitively impaired) across 17 centers in 11 countries. Frailty status was assessed using the Fried criteria, which categorize individuals into robust, pre-frail, and frail based on five factors: weakness, slow gait, unintentional weight loss, exhaustion, and low physical activity levels. Cognitive function was determined using the Montréal Cognitive Assessment. Participants completed questionnaires to evaluate perceived health (RAND-12 Health Survey, yielding both Physical and Mental Component Summaries, and EuroQOL-5D Visual Analog Scale), depressive symptoms (Patient Health Questionnaire-8), anxiety symptoms (General Anxiety Disorder scale-7), and quality of life (QoL Linear Analog Scale). Results Frailty was significantly associated with all PROs, with frail and pre-frail individuals reporting less favorable outcomes (see Figure). Cognitive function was linked to perceived health and anxiety, with patients exhibiting cognitive impairments reporting poorer perceived health and more anxiety symptoms. Conclusion This study indicates that concepts of frailty, cognitive functioning and PROs are closely related in adults with CHD. Frailty and cognition thus represent important domains when developing strategies to optimize PROs in adults with CHD. Moreover, when working with patients who are frail or cognitively impaired, healthcare workers are encouraged to consider and inquire about potential impact on PROs. Longitudinal research is needed to explore the direction of the association.