OBJECTIVE The aim of this article is to present a clinical case of severe descending mediastinitis following the insertion of three dental implants in the mandible. METHODS A 64-year-old female was treated with an implant-supported rehabilitation for her mandibular missing teeth in positions 36, 45 and 46. RESULTS Three days after the dental implant surgery, the patient complained of malaise, shiver and fever (38°C) with dysphagia and swelling of the mouth floor. The following day the patient was admitted to the hospital with a diagnosis of larynx oedema. Due to the worsening clinical conditions on day 5, she was transferred to the Thoracic Surgery Division with a diagnosis of left neck phlegmon and underwent cervicotomy. A CT scan at day 9 showed mediastinal extension of the phlegmon with initial pleural reaction. The patient then underwent cervicotomy again for drainage. On day 16, she underwent videothoracoscopy to drain a left pleural effusion. The patient was discharged on day 31. CONCLUSIONS Despite the fact that descending mediastinitis has a very high mortality rate, in the present case proper treatment was able to resolve this serious complication. It is likely that the early diagnosis and prompt treatment prevented neck and mediastinal infection diffusion. Clinicians should always keep in mind that a potential fatal infection complication may arise after routine dental implant surgery in the mandible.