AIMS: Multimorbidity is a growing problem in the general population as well as in patients with rheumatic diseases like systemic lupus erythematosus (SLE). However, patients with SLE have twice the risk of developing multimorbidity than non-SLE patients. The aim of this study was to determine the prevalence of multimorbidity in patients with SLE treated in a university hospital. METHODS: This was a cross-sectional single-centre study and included patients diagnosed and treated with SLE fulfilling the EULAR/ACR 2019 classification criteria. Multimorbidity was defined as the co-occurrence of at least two chronic diseases in an individual. The multimorbidity status was determined by a simple count of associated diseases, as well as using the Rheumatic Disease Comorbidity Index (RDCI) and the Multimorbidity Index (MMI). RESULTS: A total of 122 patients with SLE were included in the study. Multimorbidity was found in 94% of the participants. The median comorbidity score, as measured by RDCI, was 1.5, while the MMI score was 4. The most prevalent comorbidities as measured by the RDCI were hypertension (37%), other cardiovascular disease (28%), pulmonary disease (18%) and depression (9%). No correlation was found for the RDCI and MMI scores and current disease activity as measured by the SLEDAI-2K scoring system. However, there was a marked increase in the multimorbidity indices with increasing patient age. CONCLUSION: This study confirmed the high prevalence of the serious and often overlooked issue of multimorbidity in SLE patients. The RDCI and MMI were used to quantify comorbidities, as indices validated for usage in autoimmune rheumatic diseases, especially SLE. Due to the cross-sectional design of the study, it was not possible to determine the frequency of multimorbidity prior to diagnosis and its evolution with disease duration and activity. Nevertheless, the high prevalence of multimorbidity in this cohort underscores the importance of this issue.