Purpose: To determine the incidence and risk factors of late corneal graft REJECTION after penetrating keratoplasty (PKP).Methods: Records of all patients who had undergone PKP from 2002 to 2004 without immunosuppressive therapy other than systemic steroids and with at least one year of follow up were reviewed. The role of possible risk factors such as demographic factors, other host factors, donor factors, indications for PKP as well as type of REJECTION was evaluated.Results: During the study period, 295 PKPs were performed on 286 patients (176 male, 110 female). Mean age at the time of keratoplasty was 38±20 (range, 40 days to 90) years and mean follow up period was 20±10 (range 12-43) months. Graft REJECTION occurred in 94 eyes (31.8%) at an average of 7.3±6 months (range, 20 days to 39 months) after PKP.The most common type of REJECTION was endothelial (20.7%). Corneal vascularization, regrafting, anterior synechiae, irritating sutures, active inflammation, additional anterior segment procedures, history of trauma, uncontrolled glaucoma, prior graft REJECTION, recurrence of herpetic infection and eccentric grafting increased the rate of REJECTION. Patient age, donor size and bilateral transplantation had no significant influence on graft REJECTION.Conclusion: Significant risk factors for corneal graft REJECTION include corneal vascularization, anterior synechiae, irritating sutures, active inflammation, regrafting, additional surgery, trauma, uncontrolled intraocular pressure, history of graft REJECTION, recurrent herpetic infection, eccentric grafting and corneal scarring. Recipient age and donor cornea size do not seem to be risk factors for corneal graft REJECTION.