For a study, researchers sought to create the Rotterdam Transition Test (RTT), an inflammatory bowel disease (IBD)-specific knowledge questionnaire, to validate it. Investigators used a prospective longitudinal validation study as their method. There are 25 open questions about IBD, medicine, lifestyle, and the transition to adult treatment on the RTT. Inter-rater agreement was measured, and a scoring model was established. The difficulty and performance of the questions were determined using a Rasch model. To illustrate reliability, Cronbach’s alpha was utilized. RTT score was connected with patient characteristics such as age, disease, education, medication use, sickness acceptance, and independence. In 111 adolescent IBD patients, a total of 207 RTTs were evaluated. According to the scoring model, all of the questions have a kappa value of more than 0.61. Cronbach alpha reliability was good (0.81). The RTT’s mean total result was 58% (girls) and 55% (boys) of the maximum score. The RTT was effective in distinguishing between different levels of expertise. Patients who completed many RTTs throughout the transition period had higher knowledge scores. A considerably lower total RTT score was connected with male sex, poor educational level, sickness acceptance problems, and reliance on parents. The use of prednisone within 3 months and treatment without biologics was linked to considerably higher RTT scores. The presence of disease was not a significant factor. The RTT was an accurate and trustworthy tool for evaluating IBD knowledge. The RTT could be used to identify and discuss knowledge gaps in adolescents transitioning to adult healthcare who have IBD.