Cataract surgery with intraocular lens implantation is one of the most frequently performed and safest surgical procedures worldwide. But cases of visual impairment after surgery associated with impaired transparency of the IOL are described. Most often, IOL opacity occurs in the late postoperative period, several months or years after implantation and develops gradually. At the same time, there are periodic reports of sudden cloudiness of the intraocular lens during its implantation. This "behavior" of the intraocular lens is always stressful for the surgeon and makes it necessary to choose: explant the IOL or wait. Рurpose. To analyze the case of acute intraoperative opacification of the IOL. Material and methods. In January 2019, within one operating day, we recorded 5 cases of acute opacification of hydrophilic acrylic IOL (I-flex, Germany) during implantation. In the first 5 patients on this operating day, the surgeon discovered IOL opacification immediately after implantation. When the lenses were installed in the injector cartridge, the transparency of the intraocular lenses was preserved. All other IOLs implanted that day were transparent. The surgeon chose a wait and see tactic. Results. Patients were monitored, within a day, the transparency of the lenses was completely restored, the visual functions were high. Discussion. We associate IOL clouding with a sharp temperature drop, since the lenses were delivered to the clinic in the morning immediately before the operations, by car during the cold season (the air temperature outside reached -19° С). During implantation, a temperature drop occurred, which led to temporary turbidity of the polymer. However, within a few hours after the operation, the opacity was resolved and the transparency of the lenses was completely restored within a day. Key words: phacoemulsification, intraocular lens implantation, intraocular lens opacification.