Objective. To assess the prevalence of fibromyalgia in primary Sjögren's syndrome and to evaluate the clinical differences between patients affected with both primary fibromyalgia and primary Sjögren's syndrome and those affected only with primary fibromyalgia. Methods. Clinical features of fibromyalgia were evaluated in 100 consecutive outpatients with primary Sjögren's syndrome and, as controls, in 90 patients with non-insulin-dependent diabetes mellitus, in 75 patients with primary fibromyalgia and in 30 healthy subjects. Results. Fibromyalgia was recorded in 22% of patients with primary Sjögren's syndrome, in 12.2% with diabetes and in 3.3% of healthy controls. In the primary Sjögren's syndrome group the prevalence was significantly higher than in healthy controls (P < 0.01), but not significantly different than in diabetes. Moreover, primary Sjögren's syndrome with fibromyalgia and primary fibromyalgia patients did not differ with respect to the number of tender points, while the mean pain threshold was lower in the latter (P = 0.05). Purpura, hypergammaglobulinemia, rheumatoid factor, and a focus score ≥ 1 on lip biopsy were significantly more frequent in primary Sjögren's syndrome patients without than with fibromyalgia. Conclusions. As recently reported by other authors, our study confirms the moderate increase of fibromyalgia prevalence in primary Sjögren's syndrome. Typical fibromyalgic findings are quite similar to those of primary fibromyalgia, but surprisingly, primary Sjögren's syndrome patients with fibromyalgia show a less severe global involvement than those with primary Sjögren's syndrome alone.