Abstract This study retrospectively analyses paranasal sinus complications following displacement of oral implants in the maxillary sinus treated according to clinical situation by functional endoscopic sinus surgery (FESS), an intraoral approach, or a combination of both procedures. Over 5 years, 27 patients (13 male; 14 female), aged 27–73 years (mean 53.9 years), underwent treatment for postoperative complications involving the paranasal sinuses following displacement of oral implants in the maxillary sinuses. According to the complication (implant displacement, implant displacement with or without reactive sinusitis and/or with or without associated oro-antral communication), patients were treated with FESS, intraoral approach to the sinus, or FESS associated with an intraoral approach. Follow up lasted for at least 1 year with clinical and radiographic controls. 26 patients recovered completely; one patient underwent re-intervention with FESS and an intraoral approach 2 years after implant removal, due to persistent signs and symptoms of maxillary sinusitis and oro-antral communication. Postoperative recovery after the second procedure was followed by complete recovery. The results demonstrate that a rational choice of surgical protocol for the treatment of complications involving the paranasal sinuses following displacement of implants in the maxillary sinuses may lead to reliable results.