We describe a case of generalized muscle rigidity in a 2-year-old patient with Freeman-Sheldon syndrome undergoing surgery for eventration of the diaphragm after anesthetic induction with halothane and succinylcholine. Anesthetic induction was by mask with oxygen, nitrous oxide and halothane, with succinylcholine as a muscle relaxant. Approximately 10 minutes after start of induction, muscular rigidity appeared and developed rapidly, becoming severe and compromising ventilation. Tracheal intubation was attempted without success, owing to stiffness of the masseter muscles. Sodium dantrolene 2.5 mg/kg was administered and relaxation was achieved immediately for both masseter and peripheral muscles, such that the patient recovered spontaneous breathing. We conclude that there is risk of association between Freeman-Sheldon syndrome and malignant hyperthermia.