Mycotic aneurysms of the intrapetrous carotid artery are a rare complication of adjacent middle ear infections that occur by direct invasion of arterial adventitia. We report the first case of a Pseudomonas aeruginosa mycotic intrapetrous carotid aneurysm arising from mastoiditis, confirmed with middle ear cultures, presenting with high-grade bacteraemia and otorrhagia in a diabetic man. Infection was related to elective myringotomy tube placement and was initially treated with empiric antibiotics. Diagnosis required careful evaluation of imaging studies, particularly MR angiography. Resolution required aggressive debridement and carefully selected long-term intravenous antibiotics, appropriate for carefully determined antibiotic sensitivity of his pathogen, but no neurosurgical intervention. He has had no evidence of recurrence over the subsequent year. We offer our experience to highlight the dangers of invasive P aeruginosa middle ear infections in patients with diabetes to other practitioners and to encourage earlier, more aggressive intervention.