During the sinus lift procedure, undesirable perforations of the Schneiderian membrane can occur in up to 58% of cases. Several methods for their closing exist. This article presents a method of covering the perforation with a strip of oxidized regenerated cellulose (Surgicel®). One or two layers of material swell after being saturated with blood, turning into a gelatinous mass and forming a tight and mechanically resistant seal. This simple method has been successfully tested on 223 perforations of the Schneiderian membrane that occurred over a period of 58 months.