Our aim was to identify all patients with systemic lupus erythematosus (SLE) within the city of Oslo from 1999-2008 and to estimate the incidence and prevalence of SLE according to age, sex and ethnicity. Adults (16 years and over) with SLE were identified from five different sources. Only patients fulfilling four or more of the updated 1997 American College of Rheumatology (ACR) criteria were included. The incidence was stable during the nine year study period, with a mean annual incidence rate of 3.0 per 100,000 at risk (95% confidence interval (CI) 2.4-3.5). Females exhibited a bimodal pattern in age specific incidence with the first peak at 16-29 years of age and the second at 50-59 years of age. The overall prevalence was 51.8 per 100,000 population (95% CI 45.2-58.4), with 91.0 (95% CI 78.8-103.1) for females and 10.7 (95% CI 6.4-15.0) for males. The prevalence proportions for European descendants were similar to those for Asians but statistically significant lower than those for individuals adopted from non-European countries. The findings indicate a higher prevalence in Norwegians compared to Caucasians in Denmark and England. The higher prevalence of SLE in foreign adopted individuals warrants further examination.