That SS and SLE can coexist is well established. The time relationship between the two diseases is however not well known. To determine whether SS can precede SLE, we reviewed the charts of 55 patients with SS diagnosed in our department between 1975 and 1985. All 55 patients fulfilled at least four of the six preliminary criteria for SS developed by the European Study Group for SS. At entry, none met four ARA criteria for SLE and none had anti-double-stranded DNA or anti-Sm antibodies. The mean follow-up was 12 years (range 8-18 years). Four of the 55 patients developed SLE (7.5%). High titres of anti-native DNA antibodies (> 35 IU RIA, normal < 7 IU) appeared in four patients (2-11 years after the diagnosis of SS). Two of these patients fulfilled at least four ARA criteria for SLE; two others had only three criteria. Two additional patients developed anti-Sm antibodies without anti-native DNA antibodies 1 and 10 years after the initial diagnosis of SS, respectively. Both patients fulfilled six ARA criteria for SLE. At entry, anti-SSA and/or anti-SSB antibodies were present in all six SS patients and persisted subsequently. The main clinical events suggesting progression to SLE were pleuropericarditis, glomerulonephritis and focal central nervous system disease. In conclusion, SS with extraglandular components can antedate SLE by many years. Anti-native-DNA and anti-Sm antibodies should be measured when atypical clinical manifestations occur in a patient with systemic SS.