Descending necrotizing mediastinitis (DNM) is a rare complication of periodontic infection. The delay in diagnosis of DNM is believed to contribute to its high mortality rate. We report the case of a healthy 23-year-old man who was seen in the urgent care center, given the diagnosis of dental infection, prescribed penicillin, and sent home. He returned 48 hours later complaining of myalgias, purulent drainage from around his teeth, chest pain, and dyspnea. DNM was diagnosed, and aggressive treatment comprising thoracotomy, cervical incision and drainage, and antibiotics was begun. The patient responded well to treatment and was discharged from the hospital on postoperative day 20. Prompt diagnosis and immediate therapy are imperative for this rare condition.