Comparison of preoperative pachymetry with intraoperative pachymetry; evaluation of the features of intraoperative pachymetry during surgery, practical application. Material and methods. The analysis of the results of 58 operations for myopia by the FemtoLASIK method was carried out. Femtosecond laser is a Ziemer femtosecond laser. Refractive ablation – with a SCHWIND Amaris 750 S excimer laser with integrated OCP. Pachymetry was performed in the center of the cornea at the diagnostic stage and during the operation: before the formation of the flap, after the formation and removal of the flap, and after the completion of ablation. Results. It was statistically reliably revealed that intraoperative pachymetry during FemtoLASIK differs from the planned one. The regularity is associated with the process of hydration of the corneal stroma during vacuum fixation of a femtosecond laser and with the process of dehydration during laser ablation. Conclusion. The obtained results allow us to speak about step-by-step control of the corneal thickness during FemtoLASIK and comparison of the planned parameters with those measured during the operation, as a way to timely detect deviations from the operation plan and, as a result, reduce the risk of pathological corneal thinning. In cases where the values of the corneal thickness in the central zone before the operation and the flap thickness correspond to the preoperative plan, the discrepancy between the planned RST indicator and its actual measured value during the operation is not critical. Key words: FemtoLASIK, intraoperative pachymetry, residual thickness of the stromal bed, hydration, corneal dehydration.