Purpose: A heparin surface modified posterior chamber intraocular lens (IOL) was compared with a conventional polymethylmethacrylate (PMMA) IOL regarding postoperative complications caused by inflammation. Methods: Five hundred twenty-four patients from 10 different centers were included in a parallel group, double-masked, multicenter study. Results: The cumulative number of patients with inflammatory cellular deposits on their IOLs during the first postoperative year differed significantly in favor of the heparin surface modified group, with 29.8% of the patients having cellular deposits compared with 48.8% of patients in the control group. Cellular deposits were observed most frequently at 3 months after surgery, and the difference between the groups was most pronounced and statistically significant at this time. The same results were seen at 1 year, but the difference was not significant. The number of cellular deposits per patient, however, was significantly lower in the heparin surface modified group at 1 year. Cumulatively, there were significantly more patients with posterior -synechiae in the PMMA group than in the heparin surface modified group during the 1-year follow-up. Complications were few and comparable between the groups. Conclusion: The results of this study indicate that heparin surface modification reduces the inflammatory response to PMMA IOLs.