Purpose. To compare corneal astigmatism after pterygium excision, using limbal-conjunctival autograft (LCA) with and without mitomycin C (MMC) and to establish a threshold for postoperative astigmatism reduction.; Methods. Sixty-eight eyes with primary pterygium were consecutively sampled and assigned to LCA with MMC (MMC+) or LCA without MMC (MMC-). Corneal lesion length, corneal lesion area, preoperative corneal astigmatism (PRCA), and postoperative corneal astigmatism (POCA) at 1, 3, and 6 months were assessed.; Results. Thirty-six men and 24 women (60 eyes), aged between 24 and 65 years (mean +/- SD, 41 +/- 8.2 years), completed the study. Thirty-one eyes were included in the MMC+ group and 29 were in the MMC- group. Both groups showed astigmatism reduction (p < 0.05; paired, two-tailed t test) 1 month after the surgery and remained stable. No differences were found between groups in corneal lesion length, corneal lesion area, or astigmatism results at the four time points (p 9 0.05, independent t test). Preoperative corneal astigmatism showed a significant correlation with POCA at 6 months (r = 0.529; p < 0.01). According to receiver operating characteristic curve analysis, the better threshold for astigmatism reduction with the surgery was 1.05 diopters of PRCA, with 82.5% sensitivity and 80.5% specificity.; Conclusions. Both surgical procedures could have similar astigmatism results. Pterygium patients with more than 1.05 diopters of PRCA could reduce it after the surgery. Direct relationship between PRCA and POCA revealed that postoperative astigmatism reduction was partial. Therefore, for minimizing final astigmatism, preoperative values should be slightly above the threshold.