The transition from paediatric to adult diabetes care (TPA) of children/adolescents with type1 diabetes (T1D) represents a unique challenge and remains a critical phase in the T1D care pathway. This study aims to describe and understand the experience of the transition process from a participant's perspective in young adults who are living in France with T1D and to measure their satisfaction. An online questionnaire was presented to people with T1D in France on a global online participant community platform. The questionnaire was developed by a scientific committee including paediatric and adult diabetologists and refined by a group of participants. Thematic qualitative analysis was performed on the responses. A total of 104 respondents were included in the survey (mean age 24.4years [95%CI 23.8-25.0]; 61.5% female). The mean age at the time of transition was 18.4years (95%CI 17.8-18.9), and 56% of respondents had their first adult diabetology follow-up in the same institution. During TPA, of the 76 participants who experienced personal issues, 74% experienced at least one issue with their diabetes management in the months following the transition. In the following months, 61% experienced new or unexpected problems in monitoring their diabetes after transition and 44% reported unusual glycaemic imbalances, including hypoglycaemia (8%) and hyperglycaemia (9%) requiring hospitalisation. Presence of personal issues during TPA was significantly associated with occurrence of problems with diabetes management or glycaemic imbalance. Three factors identified for a successful transition were (i) early meeting with the 'adult' diabetes care team, (ii) letting the participants choose the right age to leave paediatric clinic and (iii) having good diabetes control at the beginning of the TPA process. Most young adults with T1D report experiencing issues around TPA with significant consequences on their disease management. Hence, it is necessary to identify these issues to better support them and improve diabetes management during this phase.