AIMS OF THE STUDY:To describe patterns of systemic lupus erythematosus (SLE) care and the clinical effectiveness of belimumab plus standard of care therapy in a realworld clinical setting in Switzerland.METHODS: This multicentre, observational, retrospective cohort study included adults with SLE who initiated belimumab as part of their usual care at least six months before data analysis. The primary outcome was the overall clinical response, assessed by a physician on a Physician's Global Assessment-like scale, to six months' treatment with belimumab. Secondary outcomes included improvement in disease activity, SLE manifestations and changes in corticosteroid use. RESULTS: 53 patients (81% female) from three hospitals were included. At index (belimumab initiation), 23 patients (43%) had mild, 23 (43%) had moderate, and 7 (13%) had severe SLE. Overall improvement in disease activity in patients receiving belimumab was: ≥80% in 6 patients (11%), ≥50% in 12 (23%), ≥20% in 31 (58%), <20% in 13 (25%), and no improvement in 9 (17%). Mean Safety of Estrogens in Lupus Erythematosus National Assessment-SLE Disease Activity Index score decreased from 8.0 at index to 3.6 at six months post index in the 27 patients assessed. In addition, a ≥50% improvement in arthritis, fatigue, rash, low complement (C3, C4 or total haemolytic complement activity), and anti-double-stranded deoxyribonucleic acid antibody levels was experienced six months post index by 10 (38%), 3 (16%), 6 (38%), 2 (12%) and 4 (16%) patients who presented the manifestations at index respectively. At index, 41 patients (77%) received oral corticosteroids at a mean dose of 11.6 mg/day, which decreased to 5.9 mg/ day at six months post index. Of the 31 patients receiving a high dose of corticosteroids (≥7.5 mg/day) at index, 18 required <7.5 mg/day and a further two discontinued corticosteroids at six months post index.CONCLUSIONS: This study provides real-world insight into belimumab use in clinical practice in Switzerland. In line with findings from other countries, Swiss patients with SLE who received belimumab demonstrated clinical and serological improvements in SLE and a reduction in corticosteroid use after six months of treatment.