OBJECTIVE To determine the effect of mitomycin C (MMC) on the corneal endothelium after primary pterygium surgery. METHODS This prospective, interventional, nonrandomized, observer-masked study included 46 consecutive patients (51 eyes) with primary pterygium. The bare sclera technique with 1-minute application of 0.02% MMC intraoperatively was used in all cases. The follow-up period was 3 months. Preoperative and postoperative central corneal specular microscopy was performed. The endothelial cell density, coefficient of variation of cell size, and percentage of hexagonal cells were analyzed, and the corneal thickness was measured. RESULTS The mean endothelial cell densities preoperatively and 3 months postoperatively were 2382.35 +/- 342.07 cells per square millimeter (range, 1020-3129) and 2385.02 +/- 356.83 cells per square millimeter (range, 1001-3151), respectively (P = 0.96). The mean coefficients of variation of cell size preoperatively and 3 months postoperatively were 34.31 +/- 5.62 (range, 22-49) and 35.29 +/- 7.50 (range, 22-55), respectively (P = 0.17). The mean percentages of hexagonal cells values preoperatively and 3 months postoperatively were 52.98 +/- 7.32 (range, 32-71) and 51.61 +/- 8.98 (range, 32-67), respectively (P = 0.48). The mean pachymetry measurements preoperatively and 3 months postoperatively were 506.65 +/- 36.87 microm (range, 411-583) and 502.08 +/- 41.33 microm (range, 411-593), respectively (P = 0.99). CONCLUSIONS One intraoperative application of 0.02% MMC for 1 minute after primary pterygium surgery does not seem to cause substantial changes in the corneal endothelium at 3 months.