Several connective tissue diseases such as rheumatoid arthritis and polymyositis are associated with cancer. In contrast, cancer is rarely reported in patients with Behçet disease. We report a case of lymphoma during the course of Behçet disease. Etiopathogenic factors are discussed. A 46-year-old man with a 14-year history of Behçet disease was diagnosed with non-Hodgkin malignant lymphoma of the right tonsil. He met international criteria for Behçet disease, which manifested as refractory oral ulcers requiring dapsone treatment. He achieved a complete remission of the lymphoma after three chemotherapy courses and local radiation therapy (45 Gy). At last follow-up 4 years later, he was still in complete remission.