Background: The prognosis of patients with systemic lupus erythematosus (SLE) largely depends on the severity of cumulative organ damage during the course of the disease. While Sjogren's syndrome (SS) predominantly affects exocrine glands, a considerable number of patients develop visceral organ damage. Thus, the occurrence of a secondary; SS (2°SS) in SLE patients, may result in more extensive organ damage and thereby adversely affect prognosis. Patients/Methods: 138 patients meeting the 1982 American College of Rheumatology (ACR) classification criteria for SLE were prospectively studied over a mean period of ninety months. 2°SS was diagnosed according to the 1993 European Study Group criteria and complication rates and prognosis were compared between patients with and without SS. Results: 27 patients (19%) developed SS after a mean period of 48 months. There was a gradual increase in SS prevalence over time after SLE-onset. 2°SS patients were older (mean age 41 vs 35 years, P = 0.03), had less renal disease (19% vs 38%, P = 0.04), more thrombocytopenia (26% vs 9%, P = 0.05) and similar serological profiles (including anti-SSa) as patients without SS. Overall mortality was lower in patients with SS (4% vs 13.5%, P = 0.01), while lifetable analysis showed improved survival estimates for 2°SS patients with borderline statistical significance (P = 0.06). Conclusions: 2°SS develops in about one-fifth of SLE patients in a time-dependent fashion: these patients are older, have less renal involvement and their prognosis is at least as good as for those remaining free of SS.