Background Dislocation of posterior chamber intraocular lens is one of the most common complications of intraocular lens implantation. Lens exchange is an effective solution to this unsatisfactory status. This study was conducted to analyze the possible predisposing factors for out-of-the-bag posterior chamber intraocular lens dislocation and to study the outcomes of lens exchange surgery.Methods Thirty-six consecutive patients (36 eyes) with out-of-the-bag intraocular lens dislocation who underwent posterior chamber intraocular lens exchange in Zhongshan Ophthalmic Center of Sun Yat-sen University (Guangdong,China) from January 2003 to October 2009 were included. A 6-month follow-up was completed. The causes for out-of-the-bag intraocular lens dislocation and visual outcomes of posterior chamber intraocular lens exchange were analyzed. The out-of-the-bag intraocular lens dislocation was diagnosed on the basis of the findings from slit-lamp microscope and B-ultrasound. The dislocated intraocular lens was explanted. Reimplantation of a new posterior chamber intraocular lens was performed in each case using standardized surgical procedures.Results In this study, a total of thirty-six consecutive patients (36 eyes) with out-of-the-bag intraocular lens dislocation underwent posterior chamber intraocular lens exchange surgery. Causes for out-of-the-bag intraocular lens dislocation included posterior capsule rupture during the initial cataract extraction procedure (23 eyes, 63.8%), trauma (5 eyes,13.9%), neodymium-doped yttrium aluminium garnet (Nd:YAG) laser-induced dislocation (2 eyes, 5.6%), the status after vitrectomy (2 eyes, 5.6%) and unidentifiable etiology (4 eyes, 11.1%). Symptoms of these patients mainly included decrease in visual acuity (17 cases, 47.2%), blurred vision (16 cases, 44.4%), glare (1 case, 2.8%), diplopia (1 case,2.8%), and halo (1 case, 2.8%). Intraocular lens dislocation into the posterior vitreous cavity (29 eyes, 80.5%), anterior chamber (1 eye, 2.8%) and anterior vitreous cavity (6 eyes, 16.7%) was found in this series. The foldable intraocular lenses (acrylic or silicone) were explanted from 27 eyes (75%) and rigid intraocular lenses (poly methyl methacrylate,PMMA) from 9 eyes (25%). The most common explanted intraocular lens material was single-piece acrylic (13 pieces,36.1%), followed by 3-piece acrylic (9 pieces, 25%), single-piece PMMA (9 pieces, 25%), and 3-piece silicone (5 pieces,13.9%). Uncorrected visual acuity postoperatively improved in 29 eyes (81%), unchanged in 4 eyes (11%), and worsened in 3 eyes (8%) in comparison to that before exchange operation (P=0.006). Best corrected visual acuity tended to improve, but the improvement was not significant (P=0.206). Complications related to lens exchange surgery were mainly intraocular lens redislocation (1 eye), retinal detachment (1 eye), vitreous hemorrhage (1 eye), and cystoid macular edema (1 eye).Conclusions Out-of-the-bag intraocular lens dislocation was mainly caused by posterior capsule rupture during the initial cataract extraction procedure and the foldable lens was the most common dislocated intraocular lens. In most cases, posterior chamber intraocular lens exchange surgery could provide satisfied final visual outcomes.