Schnitzler syndrome is a rare condition defined by chronic urticaria, osteosclerotic bone lesions, and monoclonal IgM gammopathy. Schnitzler syndrome can precede the onset of a true lymphoproliferative disorder including Waldenström macroglobulinemia and rarely systemic marginal zone B-cell lymphoma. We describe a case of intractable chronic urticaria accompanied by a retroperitoneal neoplasm. IgM monoclonal gammopathy, lumber pain, intermittent fever, and elevation of C-reactive protein were the clues for the diagnosis of Schnitzler syndrome. An evaluation for malignancy using systemic computed tomography scan and fluorodeoxyglucose positron emission tomography revealed the retroperitoneal tumor, and a subsequent bone-marrow aspirate confirmed the diagnosis of B-cell lymphoma. Combined rituximab and radiotherapy ameliorated the skin symptoms. This case indicates that a detailed search for malignant neoplasms might be required for the long-term management of Schnitzler syndrome, and that B-cell lymphomas may contribute to the pathogenesis of this condition.