Systemic lupus erythematosus (SLE) is the most diverse of the autoimmune diseases because it may affect any organ of the body and display a broad spectrum of clinical and immunological manifestations. Although previously considered a rare disease, SLE now appears to be relatively common in certain groups of the population. This is probably due to the development of several immunological tests that have allowed the description of many atypical or benign cases that otherwise might not be diagnosed. Furthermore, with the introduction since 1982 of a set of more sensitive criteria for SLE classification, more cases can nowadays be detected. In the present article, we review the most important data regarding the incidence and prevalence of this disease in the general population, the epidemiologic information on the patterns of disease expression in specific subsets and the studies on mortality in SLE. An important amount of information comes from the data obtained from the "Euro-Lupus Cohort," a series of 1000 patients with SLE from several European countries that have been followed prospectively since 1991.