Collagen vascular diseases and malignancies have common systemic and immune features. We report a case of a 21 year old female patient with constitutional symptoms, polyserositis, spontaneous rupture of the spleen, leukocytoclastic vasculitis and acute renal failure. The tentative diagnosis of SLE was made because she developed a positive antinuclear factor (1/640), with anti-SSA antibodies and a positive lupus anticoagulans. Two months later a cervical lymphadenopathy occurred while recieving treatment with prednisolone. A lymph node biopsy revealed morphologic features of a SLE, similar to those observed in multicentric Castleman's disease (MCD). MCD is a distinct type of a lymphoproliferative disorder of unknown etiology. The difficulties in differential diagnosis of these two diseases are discussed.