The Schnitzler syndrome is characterized by a chronic urticarial eruption with a monoclonal IgM gammopathy. The other signs of the syndrome include intermittent elevated fever, joint and/or bone pain with radiologic evidence of osteosclerosis, palpable lymph nodes, enlarged liver and/or spleen, elevated erythrocyte sedimentation rate, and leukocytosis. The mean delay to diagnosis is more than 5 years, and this syndrome is of concern to internists and many medical specialists. Patients with this syndrome are often initially considered to have lymphoma or adult-onset Still disease, which are the main differential diagnoses. However, hypocomplementic urticarial vasculitis, systemic lupus erythematosus, cryoglobulinemia, acquired C1 inhibitor deficiency, hyper IgD syndrome, chronic infantile neurologic cutaneous and articular (CINCA) syndrome, and Muckle-Wells syndrome should also be excluded, because diagnosis relies on a combination of clinical and biologic signs and there is no specific marker of the disease. The disease pursues a chronic course, and no remissions have yet been reported. Disabling skin rash, fever, and musculoskeletal involvement are the most frequent complications. Severe anemia of chronic disease is another serious complication. The most harmful complication, however, is evolution to an authentic lymphoplasmacytic malignancy, which occurs in at least 15% of patients. This hematologic transformation can occur more than 20 years after the first signs of the disease, thus patients deserve long-term follow-up. Treatment is symptomatic and unsatisfactory. The skin rash is unresponsive to treatment, and nonsteroidal antiinflammatory drugs, antihistamines, dapsone, colchicine, and psoralens and ultraviolet A (PUVA) therapy give inconstant results. Fever, arthralgia, and bone pain often respond to nonsteroidal antiinflammatory drugs. In some patients, these symptoms and/or the presence of severe inflammatory anemia require steroids and/or immunosuppressive treatment, which ameliorate inflammatory symptoms but do not change the course of the skin rash.