Schnitzler syndrome is a rare condition defined by chronic urticaria and monoclonal IgM gammopathy. Malignant evolution to Waldenström disease (WD) has been reported in several cases. We report a 49-year-old man who developed a marginal zone B-cell lymphoma (MZL) 3 years after the beginning of Schnitzler syndrome. This is the first report of MZL in association with Schnitzler syndrome. IgM gammopathy is a clue for the diagnosis of Schnitzler syndrome. This condition needs to be closely monitored; it can precede the onset of an authentic lymphoproliferative disorder including WD and rarely MZL.