Primary mycotic aneurysms of the aorta are a rare, but potentially lethal condition comprising less than 1% of all aortic aneurysms. All age groups are affected but patients younger than 50 years are most susceptible. Organisms commonly implicated in aortitis and mycotic aortic aneurysms include Salmonella species and Staphylococcus aureus(1). We present the first case report of a primary aortic mycotic aneurysm caused by Capnocytophaga canimorsus, a commensal organism found in the mouth of dogs and cats and occasionally associated with serious human infections.