Objective Gestational Trophoblastic Diseases (GTD) comprise a group of rare diseases originating from the trophoblast, affecting women of child-bearing age. Providing optimal information to patients with a rare disease is challenging, because of the small number of patients and limited clinical expertise of many healthcare professionals. Both knowledge and lack of knowledge in patients may influence illness perception. We investigated whether a web-based interactive intervention influences illness perception and knowledge in women with GTD. Design Multicenter randomized control trial. Setting General and academic hospitals in the Netherlands. Population Newly diagnosed GTD patients between 2017-2019. Methods Sixty-nine patients were randomized between direct access or postponed access to an online tool on GTD and received online questionnaires about illness perception, knowledge and anxiety. The main outcome measures were illness perception (primary outcome measure) and knowledge (secondary outcome measure) Results Patients using the online tool were satisfied with the information from the tool (92%). Although they had a higher level of knowledge compared to the control group (p = 0.006), illness perception did not change. Also, no differences in levels of anxiety, depression and distress were observed between the groups. Limitations: Participants had access to other information sources and many searched other websites. It is unknown what kind of websites were visited and when. It is unknown if the increased knowledge levels and low levels of distress will sustain over time as no long term follow-up took place. Healthcare professionals were not interviewed on how they experienced the consultation before and after using the tool by the patients. Conclusions The online tool did not change illness perception, but was shown to be valuable for newly-diagnosed GTD patients to gain knowledge. The improvement in knowledge after digital education, indicates that this tool can be used as an effective method of supporting GTD patients’ informational needs without causing extra distress.