A 59-year-old man with a long history of hypertension and diabetes was admitted to our hospital with acute type B aortic dissection 14 days after the sudden onset of back pain. The dissecting descending thoracic aorta was enlarged to 5.2 cm in diameter, and laboratory tests showed an elevated white blood cell count (15530/mm3) and an increased C-reactive protein level (19.2 mg/dl). Computed tomography performed 2 days after admission revealed rapid growth of the aortic dissection. Blood cultures obtained upon admission were positive for Salmonella. Impending rupture of the aortic dissection complicated by Salmonella infection was strongly suspected, and the patient underwent emergency surgery consisting of debridement and prosthetic graft placement covered by an omental flap. In this case, it is believed that insidious Salmonella aortitis caused acute type B aortic dissection.