A 35-year-old female patient with Behçet's disease associated with nephrotic syndrome is described. Renal biopsy specimens revealed typical features of membranous nephropathy in light microscopical, electron microscopical and immunofluorescent microscopical examinations. Circulating immune complexes (IC) phagocytized by polymorphonuclear leukocytes (PMN) in this patient were significantly increased compared with those in healthy adults. Recurrent oral aphthous ulcers had persisted for 14 years. In the course of Behçet's disease, nephrotic syndrome due to membranous nephropathy was observed. Depositions of IgA, IgM, C3 and C4 were observed in the subcutaneous arteriolar walls by immunofluorescence. It is suggested that the pathogenesis of Behçet's disease and membranous nephropathy might be due to a deposition of circulating immune complexes in various types of vascular vessels in this patient.