Clinical features of 57 eyes with proliferative vitreoretinopathy (primary PVR) that developed preoperatively were statistically analyzed and compared with a control group of 1353 eyes with non-PVR rhegmatogenous retinal detachment. The statistically significant (P less than 0.05) factors predisposing to PVR were as follows: retinal detachment for more than 1 month; aphakia (47.4% in the PVR group versus 11.1% in the control group); vitreous hemorrhage (26.3% versus 11.0%); giant tear (15.8% versus 0.8%); breaks larger than 3 disc diameters (62.1% versus 27.3%); and horseshoe tear (65.5% versus 44.9%).