We performed punctal occlusion by thermal cautery on 23 patients (45 sides, 90 puncta). One punctum on the right side was randomly assigned to deep cauterization of the punctum and vertical canaliculus, and the other punctum assigned to cauterization of the punctum only. The two treatments were assigned to the opposite puncta on the left side. One month after cauterization, the puncta that received deep cauterization were significantly more likely to have remained closed than those that received superficial cauterization (P less than .01). Survival analysis over a period of follow-up that exceeded one year after surgery, using time to examination because of a reopened punctum as the endpoint, indicated a long-term advantageous effect of deep over superficial cauterization.