Cryoglobulins are immunoglobulins that precipitate at temperatures less than 37 degrees C. They occur secondary to infectious, autoimmune, and malignant processes. In the Brouet classification, type I cryoglobulinemia is caused by hyperviscosity, whereas type II and III manifestations are caused by vasculitis in target organs (primarily skin, peripheral nerves, and kidney). New classification criteria were recently proposed that may help with study and treatment of cryoglobulinemic vasculitis (CryoVas). Hepatitis C virus is the most common cause of CryoVas and treatment with antivirals can be curative in mild cases, whereas rituximab is highly effective in treating active vasculitis in more severe cases.