BACKGROUNDNail biting is a habit with potential health implications. Patients with congenital heart disease (CHD) are at increased risk of infections, with endocarditis being a particularly significant concern. Our aim was to establish the magnitude of this modifiable potential risk factor, namely nail biting, in a contemporary cohort of adult with CHD (ACHD).METHODSOur prospective study included consecutive, unselected ACHD patients, categorised on nail-biting habits, analysing background demographics, health records, and behavioural factors.RESULTSOf the 310 patients enrolled, 101 (33 %) were found to be current nail biters. Univariate logistic analysis revealed that younger age (OR: 1.30/10 years, p = 0.002), male gender (OR: 1.73, p = 0.029), greater CHD complexity (OR: 2.15, p = 0.002) and learning disability (OR: 3.51, p = 0.031) were associated with a significantly higher risk of nail biting. Multivariable analysis confirmed that younger age (OR: 1.29, p = 0.010), greater CHD complexity (OR: 1.89, p = 0.016), obesity (OR: 1.75, p = 0.038) and learning disability (OR: 3,87, p = 0.030) were significant predictors for nail biting.CONCLUSIONA third of ACHD patients attending a tertiary centre engage in nail biting, which may have detrimental effects. Such behaviour was more prevalent among younger, obese, complex CHD patients and those with learning disability. Lifestyle education and/or modifications warrant further improvement in this growing patient population.