Aims: To study parent's levels of uncertainty related to the transfer from pediatric to adult care in adolescents with congenital heart disease (CHD) and to identify potentially correlating factors. Background: Parents acknowledge that during transition they struggle with finding ways of feeling secure in handing over the responsibility and letting go of control. Well-prepared and informed parents who feel secure are most likely better skilled to support their adolescent and to hand over the responsibility. Design: A cross-sectional study. Methods: Overall, 351 parents were included (35% response rate). Parental uncertainty was assessed using a Linear Analogue Scale (0-100). Data were collected between January - August 2016. Potential correlates were assessed using the readiness for transition questionnaire and sociodemographic data. Results: The mean parental uncertainty score was 42.5. Twenty-four percent of the parents had a very low level of uncertainty (score 0-10) and 7% had a very high level (score 91-100). Overall, 26% of the mothers and 36% of the fathers indicated that they had not started thinking of the transfer yet. The level of uncertainty was negatively associated with the level of perceived overall readiness. Adolescents' age, sex, CHD complexity, and parental age were not related to uncertainty. Conclusion: A wide range in the levels of uncertainty was found. Parents who were less involved in the care, or perceived their adolescent as readier for the transition, felt less uncertain. Still, thirty percent of the parents had not started to think about the transfer to adult care.