Fifteen patients with Horner's syndrome have been examined for the presence of upside down ptosis, and this symptom could be demonstrated in 10 of the patients. Miosis occurred in all patients, and ptosis of the upper lid was seen in 14 patients. These were the symptoms which originally enabled the diagnosis to be made. Enophthalmus was present in only 4 patients. The anatomic basis is briefly discussed, and it is advocated from the easy demonstration of upside down ptosis, together with its independence of voluntary compensation by the patient, that it should be looked for as a routine when examining for Horner's syndrome.