OBJECTIVE To assess whether excimer laser photorefractive keratectomy for myopia (PRK) induced any changes in the human corneal endothelium in the immediate postoperative period and up to one month after surgery. METHODS No-contact wide-field specular biomicroscopy of the central corneal endothelium was performed on 56 eyes of 56 patients (age 20-54 years, mean 31.3) who underwent photorefractive keratectomy for the correction of myopia ranging between 1.25 and 12.50 D (5.71 +/- 2.96 D, mean +/- SD). Images of the endothelium were obtained using the NonCon Robo endothelial biomicroscope (Konan, Hyogo, Japan), and processed to calculate the mean cell density (MCD), the coefficient of variation of cell area (CV), and the percentage of hexagonal cells (Hex%). Eyes were evaluated immediately before (preop) and after surgery (day 0), on the first two postoperative days (days 1 and 2), and after one month. RESULTS MCD was 2645 +/- 344 cells/mm2 at preop, 2609 +/- 293 cells/mm2 on day 0, 2681 +/- 320 cells/mm2 on day 1, 2629 +/- 305 cells/mm2 on day 2, and 2709 +/- 308 cells/mm2 at one month; a significant difference was found only comparing preoperative to one month data (p = 0.009). CV was 31.6 +/- 4.7 at preop, 39 +/- 7.1 on day 0 (p = 0.000001), 37.1 +/- 7.8 on day 1 (p = 0.00005), 43.4 +/- 13.1 on day 2 (p = 0.000001), and 34.7 +/- 5.8 on one month (p = 0.0006). Hex% was 61.9 +/- 7.1 at preop, 58 +/- 7.3 on day 0 (p = 0.002), 58.5 +/- 8.5 on day 1 (p = 0.015), 57.1 +/- 8.5 on day 2 (p = 0.00004), and 59.3 +/- 7.5 at one month (p = 0.002). No correlations were found between ablation depth and endothelial changes. CONCLUSIONS Endothelial cell density was not reduced by PRK in the immediate postoperative period. Changes in morphological indices like CV and Hex% indicate that the photoablation causes some kind of damage to the endothelial cells.