Title: The influence of intraocular monofocal lens position during ultrasound phacoemulsification cataract surgery on the occurrence of dysphotopsia Objectives: The aim of the study was to examine the incidence and intensity of positive and negative dysphotopsias in each patient group depending on the position of the intraocular lens (IOL) (vertical, horizontal, superonasal, inferonasal). Additionally, the aim is to investigate whether there is a correlation between positive and negative dysphotopsias and the position of the IOL. Study Design: Cross sectional study. Participants and methods: This study included 80 patients divided into four groups based on the IOL position, who underwent ultrasound phacoemulsification cataract surgery. For each patient, age, gender, the operated eye, keratorefractometry, and the best-corrected visual acuity on the day and one month after cataract surgery were recorded. Optical biometry was performed, and axial length, anterior chamber depth and IOL power were measured using the IOL Master 700 device. All patients underwent monofocal, single-piece, hydrophobic acrylic IOL implantation. In the first group, the IOL was implanted vertically, in the second group horizontally, in the third group superonasally, and in the fourth group inferonasally. Each group consisted of 20 participants. The control group comprised patients with horizontally implanted IOL. Results: Positive dysphotopsias appeared in 21 (26,3 %) patients, with no significant difference according to IOL position (Fisherov egzaktni test, P =0,63). Negative dysphotopsias were recorded in 9 (11,3% ) patients. Significantly higher negative dysphotopsias were associated with inferonasal and superonasal IOL positions (Fisher's exact test, P =0,01). There was no significant difference in the intensity of positive (Kruskal-Wallis test, P =0,33) and negative dysphotopsias (Kruskal-Wallis test, P =0,20), among patients experiencing dysphotopsias, concerning the IOL position. Conclusion: There was a significant correlation between the position of IOL and the incidence of negative dysphotopsia in patients. Higher incidence of negative dysphotopsia has been associated with inferonasal and superonasal IOL positions. This suggests that the perception of negative dysphotopsia after surgery may be affected by the position of the lens. However, no significant difference was found in the intensity of positive and negative dysphotopsia in patients with dysphotopsia, in relation to the position of the IOL.