Sjogren's syndrome (SS) is an autoimmune disease characterized by a chronic inflammatory response mainly localized to the lacrimal and salivary glands. However, it sometimes involves extraglandular organs culminating in systemic disorders. Hematological abnormalities are not uncommon, although they rarely have clinical significance. In this study we examined 99 patients with primary SS who visited our hospital during 1989 to 1999. Patient's mean age was 54.1 years and 95 out of 99 were female. Lymphopenia and leukopenia was noted in 35 patients (35.3%) and 26 patients (26.2%) respectively, and 7 patients (7.1%) had thrombocytopenia. 43 patients (43.4%) had either of these hematological abnormalities. Patients with lymphopenia showed significantly low frequency of arthralgia and anti-SS-A/B antibody was more common in this group. Only one patient in this group required prednisolone therapy because of polyarthritis and general fatigue while others needed no specific therapy. Patients with thrombocytopenia were significantly younger and a male/female ratio was higher than those without this abnormality. They had higher tendency to accompany with skin eruption, positive anti-SS-B antibody, anti-nuclear antibody and rheumatoid factor. Three out of 8 patients with thrombocytopenia were treated with prednisolone according to the protocol for idiopathic thrombocytopenic purpura. All of 3 patients had positive PA-IgG and normocellular bone marrow. Autoimmune mechanism such as polyclonal B cell activation may play a role in the pathogenesis of thrombocytopenia.