Background: Several risk factors for severe COVID-19 have been identified 1 . An important question is whether in addition to these generic risk factors, patients with a potentially altered immune response, either by disease (inflammatory rheumatic diseases (IRDs)) or use of immunomodulatory agents (IA), carry a higher or lower risk of severe COVID-19. In addition, several other potential risk factors for severe COVID-19 have been suggested, such as vitamin D status and specific medication (NSAIDs, ACE-inhibitors) 2 . Objectives: To identify risk factors for severe COVID-19, requiring hospitalization, in patients with IRDs. Methods: Multicenter, unmatched nested case control study in four rheumatology centers in the Netherlands. Cases are IRD patients requiring hospitalization for COVID-19 between March 1 st 2020 and May 31 st 2020. Control patients are IRD patients not hospitalized for COVID-19 within this period and were included in a 1:4 ratio. Patient-, disease- and treatment characteristics were extracted (still ongoing) from electronic patient files, and a questionnaire was used to collect additional data (e.g. on behavioral aspects). Potential risk factors for severe COVID-19 were analyzed using unconditional logistic regression, corrected for confounders. Results: 77 cases and 198 controls were included. 26 case patients died as a result of COVID-19, 14 were admitted to the ICU. Crude ORs for female sex, age, BMI and presence of one or more comorbidities were 0.46 (95% CI 0.27-0.29), 1.1 (95%CI 1.0-1.1), 1.0 (95%CI 0.98-1.1) and 3.0 (95%CI 1.7-5.2) respectively. Table 1 displays corrected OR, highlighted when OR <0.5/>2.0. Corrected ORs were not significantly increased for any IRD, but a trend for gout was present. Use of hydroxychloroquine (HCQ) shows a protective effect, while use of other csDMARDs than methotrexate or HCQ leads to a higher risk of severe COVID-19. Trends were present for increased risk for rituximab (RTX), glucocorticoids and ACE inhibitors, and protective effect for IL-6R ...