· AIM: To investigate risk factors for the development of membrane formation in the anterior chamber after pha coemulsification.· METHODS: A total of 1356 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, perioperative complications (capsulorhexis rupture, zonular dialysis, posterior capsule rupture with vitreous loss), location of IOL placement and postoperative complications (intraocular pressure changes, synechia formation) 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 1st and 7th 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 (P＜0.05). In the membrane-forming group, mean phaco time was 2.4minute and mean effective phaco time was 32.8 seconds,compared to 1.8 minute and 22.1 seconds in the membrane-free group. Both parameters were significantly longer in the membrane-forming group (P＜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 (P＜0.05). Other risk factors were not statistically different between membrane-forming and membrane-free patients. On postoperative first and 7th day, the mean best corrected visual acuity in the membrane-forming group was 0.2 and 0.4 respectively, versus 0.4 and 0.6 in the membrane-free group on Snellen chard (P＜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 were risk factors which significantly assocaiated with postoperative fibrinous membrane formation in the anterior chamber.