Using the Cochet-Bonnet esthesiometer, we evaluated the corneal sensation of 11 patients with unilateral Adie's tonic pupil. We eliminated six other patients with bilateral Adie's pupil or disease that lowered corneal sensation. An observed unfamiliar with each patient's condition tested 12 clock hour positions in the midperiphery in both eyes of all patients. We studied 30 normal subjects (60 eyes) in a similar fashion. Of those 11 patients with unilateral Adie's syndrome, ten had a regional decrease in corneal sensation. The 30 normal subjects examined did not exhibit any significant decrease in corneal sensation in any areas. Our study supports the concept that the lesion of Adie's tonic pupil is in the ciliary ganglion or short location where the innervation of the iris sphincter and corneal sensation are found together.