Abstract Objective SLE is characterized by relapses and remissions. We aimed to describe the frequency, type and time to flare in a cohort of SLE patients. Methods SLE patients with one or more ‘A’ or ‘B’ BILAG-2004 systems meeting flare criteria (‘new’ or ‘worse’ items) and requiring an increase in immunosuppression were recruited from nine UK centres and assessed at baseline and monthly for 9 months. Subsequent flares were defined as: severe (any ‘A’ irrespective of number of ‘B’ flares), moderate (two or more ‘B’ without any ‘A’ flares) and mild (one ‘B’). Results Of the 100 patients, 94% were female, 61% White Caucasians, mean age (s.d.) was 40.7 years (12.7) and mean disease duration (s.d.) was 9.3 years (8.1). A total of 195 flares re-occurred in 76 patients over 781 monthly assessments (flare rate of 0.25/patient-month). There were 37 severe flares, 32 moderate flares and 126 mild flares. By 1 month, 22% had a mild/moderate/severe flare and 22% had a severe flare by 7 months. The median time to any ‘A’ or ‘B’ flare was 4 months. Severe/moderate flares tended to be in the system(s) affected at baseline, whereas mild flares could affect any system. Conclusion . In a population with active SLE we observed an ongoing rate of flares from early in the follow-up period with moderate–severe flares being due to an inability to fully control the disease. This real-world population study demonstrates the limitations of current treatments and provides a useful reference population from which to inform future clinical trial design.