This study presents the case of a patient who required antrostomy under general anesthesia to treat a sinus lift complication. The patient was a 43-year-old woman with no systemic abnormalities who underwent maxillary sinus lift surgery associated with mineralized bovine bone graft. The Schneiderian membrane was perforated during the procedure, and the rupture was treated with collagen membranes to close the wound and contain the biomaterial, preventing its dispersion. The patient developed a maxillary sinus infection 7 days after surgery. This infection was initially treated with 875 mg amoxicillin combined with 125 mg clavulanic acid. Although the initial infection did not worsen, the patient developed maxillary sinusitis. Thirty days after the onset of the initial infection, the patient underwent an intraoral surgery under local anesthesia to remove the biomaterial and clean the sinus cavity. Despite this procedure, maxillary ostial patency was still compromised, and antrostomy was performed endoscopically in a hospital setting under general anesthesia. This procedure resolved the sinus infection. Then, 12 months after hospitalization, the patient was treated with another sinus graft surgery without postoperative complications. The treatment of sinus infections caused by the graft surgery may require early and active intervention with antibiotics, graft removal, and antrostomy to prevent major complications.