To evaluate the time course and extent of the restenosis that occurs after an endoscopic modified Lothrop procedure (EMLP) and to identify factors that contribute to this process. : Retrospective study of prospectively collected data. Seventy-seven consecutive patients undergoing EMLP between November 1998 and June 2005 with frontal ostium measurements documented intraoperatively and at follow-up visits for a minimum of 12 months were included. Data on patient demographics, medical history, comorbidities, and computed tomography scans were collected. Significant restenosis of the frontal sinus neo-ostia was defined as a loss of more than 60% of the original intraoperative area. The mean follow-up in our cohort was 29.2 months. Twenty-two patients were identified with increased stenosis, all of which arose within the first 12 months postsurgery. Nine of these 22 patients required revision EMLP. In all patients, the new frontal ostium narrowed at 1 year by an average of 33% (from 290 to 191 mm2, confidence interval 159-223 mm2). Restenosis and revision surgery are partly predicted by the presence of eosinophilic mucin chronic rhinosinusitis as demonstrated by logistic regression analysis. Linear regression analysis confirmed that the intraoperative frontal ostium size determines the frontal ostium area at 1 year. This study provides benchmarking values for the time course of the frontal ostium area after EMLP for normal wound healing and increased stenosis. On the basis of our results, patients with a higher risk for developing restenosis and of having revision surgery can be identified preoperatively and during the early postoperative period to facilitate special postoperative care.