Background Corticosteroids are a mainstay of the treatment of moderately severe relapses of ulcerative colitis, yet almost 50% of patients do not respond fully to these and risk prolonged steroid use and side effects. There is a lack of clarity about the definitions of steroid resistance, the optimum choice of treatment, and patient and health-care professional treatment preferences. Objectives The overall aim of this research was to understand how steroid-resistant ulcerative colitis is managed in adult secondary care and how current practice compares with patient and health-care professional preferences. Design A mixed-methods study, including an online survey, qualitative interviews and discrete choice experiments. Setting NHS inflammatory bowel disease services in the UK. Participants Adults with ulcerative colitis and health-care professionals treating inflammatory bowel disease. Results We carried out a survey of health-care professionals (n = 168), qualitative interviews with health-care professionals (n = 20) and patients (n = 33), discrete choice experiments with health-care professionals (n = 116) and patients (n = 115), and a multistakeholder workshop (n = 9). The interviews with and survey of health-care professionals showed that most health-care professionals define steroid resistance as an incomplete response to 40 mg per day of prednisolone after 2 weeks. The survey also found that anti-tumour necrosis factor drugs (particularly infliximab) are the most frequently offered drugs across most steroid-resistant (and steroid-dependent) patient scenarios, but they are less frequently offered to thiopurine-naive patients. Patient interviews identified several factors influencing their treatment choices, including effectiveness of treatment, recommendations from health-care professionals, route of administration and side effects. Over time, depending on the severity and duration of symptoms and, crucially, as medical treatment options become exhausted, patients are willing to try alternative treatments and, eventually, to undergo surgery. The discrete choice experiments found that the probability of remission and of side effects strongly influences the treatment choices of both patients and health-care professionals. Patients are less likely to choose a treatment that takes longer to improve symptoms. Health-care professionals are willing to make difficult compromises by tolerating greater safety risks in exchange for therapeutic benefits. The treatments ranked most positively by patients were infliximab and tofacitinib (each preferred by 38% of patients), and the predicted probability of uptake by health-care professionals was greatest for infliximab (62%). Limitations The survey and the discrete choice experiments with patients and health-care professionals are limited by their relatively small sample sizes. The qualitative studies are subject to selection bias. The timing of the different substudies, both before and during the COVID-19 pandemic, is a potential limitation. Conclusions We have identified factors influencing treatment decisions for steroid-resistant ulcerative colitis and the characteristics to consider when choosing treatments to evaluate in future randomised controlled trials. The findings may be used to improve discussions between patients and health-care professionals when they review treatment options for steroid-resistant ulcerative colitis. Future work This research highlights the need for consensus work to establish an agreed definition of steroid resistance in ulcerative colitis and a greater understanding of the optimal use of tofacitinib and surgery for this patient group. A randomised controlled trial comparing infliximab with tofacitinib is also recommended. Funding This project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 26, No. 41. See the NIHR Journals Library website for further project information.