One of the characteristics of systemic lupus erythematosus (SLE) is the large inter- and intra-individual variability of the clinical course. Lupus nephritis is no exception. Some patients with kidney involvement may show rapid progression to renal failure, others may enter complete and stable remission after adequate therapy while a number of other patients, with similar clinical and histological pattern at presentation, may alternate periods of clinical quiescence with renal exacerbations of different severity. In this paper we focus on the incidence, the prognostic significance and the treatment of renal flares in patients with SLE nephritis.