OBJECTIVES: Using prospectively collected registry data to investigate sick leave (sickness benefit and sickness compensation) over a 7-yr period in patients with AS in comparison with population-based controls matched for age, sex and residential area.

METHODS: We investigated 122 (21 women and 101 men) outpatients with AS in South Sweden, born 1942 or later, from rheumatology specialist care for their sick leave during a 7-yr period. Mean (S.D.) age was 43 (11) yrs and mean (S.D.) disease duration was 20 (11) yrs. Two controls per case, matched for age, sex and residential area were selected from the Swedish National Population Register. Data concerning sick leave for cases and controls, based on the subjects' unique 10-digit personal identification number, were retrieved from the national register of the Swedish Social Insurance Agency.

RESULTS: More AS patients than controls were registered for sickness benefit (52 vs 36%, P < 0.01) and sickness compensation (42 vs 11%, P < 0.001). Cases had an increased risk for sick leave compared with controls with a relative risk of 1.8; 95% CI 1.5, 2.1; and cases had more days with sick leave than controls (median number of more days per year 30; 95% CI 2, 72).

CONCLUSIONS: Using the Swedish Social Insurance Agency's registers for sick leave, we found that patients with AS in rheumatology specialist care in South Sweden have an increased level of sick leave compared with controls. These population-based registers have a great potential for studies of the effects of different interventions on sick leave. © 2009 The Author(s).