Maintenance of wide pupillary dilation during vitreoretinal surgery can be important in successful completion of the operation. This study identified factors associated with intraoperative miosis. Also, flurbiprofen, a topically applied nonsteroidal anti-inflammatory agent, was evaluated for its efficacy in preventing intraoperative miosis in a prospective, randomized study of 99 consecutive patients. Factors associated with intraoperative miosis included duration of surgery greater than 90 minutes, preoperative afferent pupillary defect, and recent previous surgery. Preoperative treatment with flurbiprofen did not decrease the risk of intraoperative miosis.