Systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) can coexist in patients. The aim of this study was to investigate the clinical, laboratory, and serologic features of the association of the two diseases. Data from 56 patients having both SS and SLE were analyzed, with special emphasis on their clinical, laboratory, and serologic features. Data from 50 patients with SLE and 50 patients with SS served as control subjects. The mean age in SS-SLE group was lower than in patients with SS but higher than patients with SLE. When SLE and SS were associated, presence of rheumatoid factor was less frequent, whereas anti-Ro/SS-A, anti-La/SS-B, antinuclear, anti-DNA, and antiphospholipid autoantibodies appeared more often. Antiphospholipid syndrome, anemia, leucopenia, and lymphopenia were more frequent in the associated disease than in patients with SS alone. In SS-SLE patients, pulmonary, renal, skin, central nervous system involvement, and serositis occurred more often than in patients with SS alone. Thyroiditis, autoantibodies to Ro/SS-A, La/SS-B and ds-DNA was more frequent in the SS-SLE group than in patients with SLE. Genetic background of the patients did not differ significantly. In conclusion, characteristic clinical, laboratory and serologic features distinguish between the association of SS and SLE and the primary forms of these two diseases.