Mastocytosis is an acquired orphan disease characterized by the abnormal accumulation of mast cells responsible for organ failure and systemic symptoms. Cytoreductive drugs have been shown to be effective, but have rarely resulted in complete or long-term remission. We report two patients with advanced systemic mastocytosis (SM) who were treated successfully with thalidomide, given at the maximal tolerated dosage. B and C-findings as well as clinical symptoms rapidly improved. After a follow-up of more than 1 year, the patients remained in partial remission. Thalidomide seems to be an active drug in advanced SM. However, clinical trials are warranted to define its efficacy and safety profiles.