AIM:To identify risk factors for the development of posterior synechiae of the iris (PSI) after 23-gauge phacovitrectomy.METHODS:A retrospective chart review was performed in consecutive Asian patients treated with 23-gauge phacovitrectomy with a 3-piece intraocular lens (IOL) or a single-piece 4 haptics IOL.RESULTS:A total of 263 eyes from 242 patients were included in the study. Postoperative PSI was identified in 16 (6.1%) eyes. In multivariate analysis, C3F8 gas tamponade, oil tamponade, and long operation time were significantly associated with PSI formation. There was no difference in the incidence of PSI between the groups using two different types of IOL (P=0.779). CONLUSION:C3F8 gas or oil tamponade and long operation time increased the incidence of PSI after 23-gauge phacovitrectomy. The single-piece 4 haptics IOL, in lieu of a 3-piece IOL, may be inserted into the capsular bag with a comparable incidence of PSI.