BACKGROUND: Vitamin D status varies with geographic location and no studies of vitamin D in systemic lupus erythematosus (SLE) have been reported in the Southern Hemisphere. OBJECTIVES: To assess the prevalence of vitamin D deficiency in an Australian SLE cohort, and its relationship with disease activity. METHODS: Data were collected prospectively on 119 consecutive patients with SLE in the Monash Lupus Clinic in Melbourne, Australia, between January 2007 and January 2013. Patients had simultaneous serum 25-hydroxyvitamin D concentration and disease activity (SLEDAI-2K) recorded. Statistical methods were used to determine the correlation of serum vitamin D level and disease activity both at baseline and at a subsequent time point. Adjustments were made for the use of glucocorticoids, immunosuppressants and vitamin D supplementation. RESULTS: Vitamin D deficiency (10) at the subsequent time point (univariable OR 3.1, 95 CI 1.4 to 6.8, p=0.004). CONCLUSIONS: In Australian patients with SLE, low vitamin D was associated with a higher disease activity and an increase in serum vitamin D was associated with reduced disease activity over time. The therapeutic effect of vitamin D in SLE should be further assessed in interventional studies.