Purpose: To compare the effects of preoperative use of topical anti-inflammatory prednisolone acetate, ketorolac tromethamine, nepafenac and placebo, on the maintenance of intraoperative mydriasis during cataract surgery. Design: Randomized clinical trial. Materials and Methods: This single-center, masked, randomized clinical study comprised 140 patients scheduled for cataract surgery. Patients (35 in each group) were randomized to receive placebo, prednisolone acetate, ketorolac tromethamine 0.4% or nepafenac. These eye drops were administered three times daily for the two days prior to surgery. The pupillary diameters were measured by the surgeon using a compass prior to the corneal section and at the end of surgery. The primary outcome was the number of patients with pupil >= 6mm at the end of the surgery; the secondary outcome was the number of patients with pupil >= 6mm at the beginning of the surgery. Results: All the patients achieved pupil >= 6mm at the beginning of the surgery. The number of patients in the prednisolone (29/35), nepafenac (31/35) and ketorolac (30/35) groups with pupil >= 6mm was greater than in the placebo group in the maintenance of intraoperative mydriasis (19/35 - P =0.003). There was no statistical difference among the prednisolone, nepafenac and ketorolac groups in the maintenance of intraoperative mydriasis (P =. 791). There were no complications during surgery or related to the preoperative use of the eye drops. Conclusion: Preoperative use of ketorolac, prednisolone and nepafenac was effective in maintaining intraoperative mydriasis when compared with placebo.604277281