A 55-year-old male patient was referred to our clinic with signs and symptoms of recurring sinusitis after a right maxillary sinus floor augmentation for implantological purposes. Investigations showed an antibiotic-resistant ethmoidomaxillary sinusitis resulting from bone graft infection and displacement of previously inserted xenograft material into the maxillary sinus. The patient thus underwent a surgical procedure combining nasal endoscopy and oral surgery in order to remove the infected graft and restore sinusal drainage. The procedure was apparently successful but sinusitis relapsed after surgery and persisted despite 2 weeks of antibiotic therapy and local medications. A CT scan showed persistence of grafting fragments in the maxillary sinus. A new surgical procedure was scheduled while a more accurate endoscopic local medication was performed. Six hours after the treatment, the patient spontaneously expelled the fragments and promptly recovered. The patient successfully underwent another maxillary sinus floor augmentation procedure 6 months later.