Aim: To present a rare but clinically significant complication to sinus floor elevation (SFE) using the transcrestal technique. Materials and methods: Transcrestal SFE with simultaneous implant placement was performed in the maxillary right second premolar region of a healthy 70-year-old woman with no history of a bleeding disorder. Results: The patient reported to the emergency care unit a few hours after the surgery with ongoing bleeding and progressive swelling of especially the right side of the midface. The buccal swelling did not allow the patient to close her mouth and the discoloration extended to the sternum. A computed tomography scan showed pronounced swelling of the facial soft tissue and the right sinus cavity completely filled with blood. The patient was kept hospitalised for 3 days until regression of the swelling was attained and acceptable oral function was regained. Conclusion: Transcrestal SFE is often recommended to the less experienced surgeon before the lateral window technique due to fewer complications and lower morbidity. The present case illustrates that severe complications may accompany transcrestal SFE. Although rare, clinicians performing SFE should be aware of this potential risk. Keywords: complication, dental implants, haemorrhage, sinus floor elevation, vascularisation