Schnitzler syndrome or Schnitzler's syndrome is a rare disease characterised by onset around middle age of chronic hives (urticaria) and periodic fever, bone and joint pain (sometimes with joint inflammation), weight loss, malaise, fatigue, swollen lymph glands and enlarged spleen and liver.

[3] Blood tests show a high concentration of specific gamma-globulins (monoclonal gammopathy) of the IgM type.

Signs of inflammation are often present: these include an increased white blood cell count (leukocytosis) and a raised erythrocyte sedimentation rate and C-reactive protein.

[1] The Lipsker criteria require hives, the presence of monoclonal IgM, and at least 2 of the following: fever, joint pain or arthritis, bone pain, swollen lymph nodes, enlarged spleen or liver, elevated erythrocyte sedimentation rate, high levels of white blood cells, and findings of problems in bone imaging.

[1][5] Other conditions which can cause periodic fevers, paraproteins or chronic hives that should be ruled out, include (and are not limited to) autoimmune or autoinflammatory disorders such as adult-onset Still's disease, angioedema, hematological disorders such as lymphoma or monoclonal gammopathy of undetermined significance (MGUS), other causes of hives, cryoglobulinemia, mastocytosis, chronic neonatal onset multisystem inflammatory disease or Muckle–Wells syndrome.

[1] A 2020 review reported that canakinumab was "an effective long-term treatment with a favorable safety profile in patients with Schnitzler syndrome".

[14] A Delphi study on the taxonomy and definition of auto-inflammatory diseases, published in 2018, considered the alternative name "late onset gammopathy with recurrent urticaria and fever" but this received little support.