Aims: To evaluate the effects of melatonin premedication on anxiety and pain scores of patients, operating conditions, and intraocular pressure during cataract surgery under topical anesthesia. Materials and Methods: Sixty patients were randomly assigned to receive either sublingual melatonin 3 mg or placebo 60 min before surgery. Verbal anxiety scores and verbal pain scores, heart rate, systolic and diastolic blood pressure, intraocular pressure, and quality of operating conditions were recorded. Results: Melatonin significantly reduced the anxiety scores (median, interquartile range) from 5 and 5-3 to 3 and 2-4 after premedication and to 3 and 2-3 during surgery and to 0 and 0-1 postoperatively before discharge from the recovery room. There were significant differences between two groups in anxiety scores after premedication (95% CI 3-3.5; P = 0.023), intraoperatively (95% CI 2.5-3.5; P = 0.007), and postoperatively (95% CI 0.5-1; P = 0.007). The surgeon reported better quality of operating conditions in the melatonin group (P = 0.001). No significant difference in intraoperative and postoperative pain scores, intraocular pressure, heart rate, and systolic and diastolic blood pressure between two groups was recorded. Conclusion: Sublingual melatonin premedication for patients undergoing cataract surgery under topical anesthesia reduced the anxiety scores in patients and provided excellent operating conditions.