To investigate the risk factors for the development of membrane formation in the anterior chamber after phacoemulsification. METHODS: A total of 1 356 patients who underwent phacoemulsification with implantation of single piece polymethyl methacrylate (PMMA) IOL were prospectively evaluated. Presence of pseudoexfoliation syndrome, nuclear hardness, pupil size, phaco time, effective phaco time, systemic diseases, postoperative complications (capsulorhexis rupture, zonular dialysis, posterior capsule rupture with vitreous loss), location of IOL placement and postoperative complications(intraocular pressurechanges, synechiaformation) were analyzed as risk factors for development of membrane formation. ·RESULTS: In 111 (8.1%) patients postoperative fibrinous anterior uveitis with membrane formation was observed. The mean time for membrane formation was postoperative second day (range postoperative 1^st and 7^th day). Mean duration of the presence of membrane was 5.2 days (range 1 to 48 days). Among the patients who had membrane formation, +4 hardness of the nucleus was present in 45%, while it was present in only 13.5% of patients who did not have membrane formation. The difference was statistically significant ( <0.05). In the membrane-forming group, mean phaco time was 2.4 minutes and mean effective phaco time was 32.8 seconds, compared to 1.8 minutes and 22.1 seconds in the membrane-free group. Both parameters were significantly longer in the membrane-forming group ( <0.05). Posterior capsule rupture with vitreous loss and sulcus implantation of IOL was seen in 33% of membrane-forming patients and in 11%of membrane-free patients ( <0.05). Other risk factors were not statistically different between membrane-forming and membrane-free patients. On postoperative first and 7^th day, the mean best corrected visual acuity in the membraneforming group was 0.2 and 0.4 respectively, versus 0.4 and 0.6 in the membrane-free group on Snellen chard ( <0.05). But three months after surgery, the best corrected visual acuity was similar between the membrane-forming and membrane- free patients (0.8 and 0.9 respectively). ·CONCLUSION: Higher nucleus hardness, longer phaco time and effective phaco time, and posterior capsule rupture during surgery are risk factors which significantly associated with postoperative fibrinous membrane formation in the anterior chamber.