Relapses, characterised by episodes of new or worsening neurological symptoms, are the defining feature of relapsing-remitting multiple sclerosis (RRMS), the most common MS phenotype (Kalincik, 2015). In most cases, symptoms worsen for one to two weeks and subside over the following two to four weeks without treatment (Ramo-Tello et al., 2021). Short-term corticosteroid (CC) therapy, using high-dose methylprednisolone, is the widely accepted treatment standard (Hemmer, 2021; Ramo-Tello et al., 2021). Compared to placebo, CC lead to a faster reduction of symptoms in about 25 of 100 treated patients (Citterio et al., 2000). However, evidence for long-term benefits, such as the prevention of new relapses and long-term progression, is insufficient (Citterio et al., 2000; Gal et al., 2015). CC is associated with adverse events that are potentially harmful, including insomnia and gastrointestinal complaints (Citterio et al., 2000; Gal et al., 2015). Considering the discrepancy between the lack of high-quality evidence on high-dose CC and possible adverse events, patients need to be involved in relapse therapy decision-making (Köpke et al., 2004). Patient engagement and shared decision-making can improve MS disease management and optimise health outcomes (Rahn et al., 2020). To make informed decisions about relapse management, people with MS (PwMS) need adequate information. Reliable, up-to-date information and MS knowledge can empower patients, improve satisfaction with care and lower decisional conflicts (Colligan et al., 2017). A Cochrane review of interventions evaluating the effectiveness of information provision for PwMS highlights that patients’ MS-related knowledge is poor, showing the importance of providing information and promoting patients’ knowledge (Köpke et al., 2018). Very few MS educational programmes have been developed and rigorously evaluated in recent years, addressing unmet information needs in PwMS (Köpke et al., 2018). A randomised-controlled trial (RCT) with 150 PwMS showed that an evidence-based educational programme on relapse management leads to relevant changes in participants’ relapse management and more autonomous decision-making (Köpke et al., 2009). Besides the importance of MS knowledge in the clinical setting as a basis for informed decision-making, knowledge also plays a major role in research as an outcome measure assessing the efficacy of educational interventions. Currently, there is no validated instrument specifically measuring relapse knowledge in PwMS. Previous work focused on the development of questionnaires and scoring scales assessing general MS knowledge (Bessing et al., 2021; Maybury and Brewint, 1984), knowledge about disease-modifying treatment (Abolfazli et al., 2014) or risk knowledge (Heesen et al., 2004, 2015, 2017) in newly diagnosed PwMS (Giordano et al., 2010), or parents of children with MS (Uccelli et al., 2013). To provide a feasible tool for relapse management interventions, we developed the self-administered relapse knowledge questionnaire (RKQ), aiming to assess relapse knowledge in PwMS. Along with another questionnaire, the RKQ was tested in an online survey in 2019 (Haker et al., 2021). The focus of Haker et al.'s paper is the validation of the Planned Behaviour in MS – Relapses (PBMS-R) questionnaire. This paper describes the development process and validation of the RKQ, to be applied as an outcome instrument for educational interventions on relapse management. The overall aim of the development and validation process was to assess relapse knowledge in PwMS to address knowledge needs and obtain a helpful outcome instrument for the underlying educational intervention POWER@MS2.