BACKGROUND Behçet's syndrome rarely occurs in North America and Central Europe (incidence: 1 : 500,000), whereas it is more frequently seen in Japan and Mediterranean countries (incidence: 1 : 10,000). The diagnosis is based on the detection of symptoms and clinical signs. Orogenital aphthosis, anterior and posterior uveitides that frequently cause loss of vision are considered to be primary symptoms. Dermatologic manifestations, i.e., erythema nodosum, vascular lesions (angio-Behçet's syndrome), gastrointestinal ulcers and neurologic involvement, can be observed. HLA B5 is found in some of the patients with Behçet's syndrome. Administration of chlorambucil, a cytotoxic compound, is an effective form of treatment of symptoms and complications of Behçet's syndrome. METHODS The present article describes the course of a female and a male patient who were 39 and 23 years old when Behçet's syndrome was diagnosed for the first time. Treatment with chlorambucil was started in the early 1990s and continued for a period of 9 1/2 and 3(3/4) years, respectively, with the symptoms remitting during and after this therapy. Approximately 10 years after the start of treatment with chlorambucil, the patients' symptoms changed. The female patient who was first diagnosed having Behçet's syndrome at the age of 39 years developed rheumatoid arthritis with joint destruction. Her symptoms could be controlled in the long term by oral administration of prednisone, at doses below the Cushing threshold combined with methotrexate. The male patient who was first diagnosed having Behçet's syndrome at the age of 23 years developed systemic vasculitis remitting during low-dose treatment with prednisone. CONCLUSIONS Immunosuppressive therapy with chlorambucil administered over several years often induces remission of Behçet's syndrome. However, both case reports indicate that symptoms can change from Behçet's syndrome to systemic vasculitis or rheumatoid arthritis.