Stellate ganglion block, due to its wide range of indications, is the most widely practiced procedure in pain clinics. We experienced the case of a 44-year-old female patient who developed prolonged Horner's syndrome after the use of stellate ganglion block. The patient recovered spontaneously from the Horner's syndrome after 12 months. If Horner's syndrome should occur, its etiology will need to be assessed. It is also important to assure the patient they will recover from the complication within a year.