Author(s): J Maundrell, S Fletcher, P Roberts, A Stein, M Lambie Format Abstract Bacillus Calmette-Guérin (BCG) is a live attenuated strain of Mycobacterium bovis that has been widely used for the treatment of superficial transitional cell carcinoma of the bladder. We describe a rare case of supra-renal mycotic aortic aneurysm secondary to BCG instillation in a 75-year-old male. Patients presenting with systemic symptoms post-instillation, possibly with an aneurysm, should raise suspicion of BCG dissemination, which requires early instigation of anti-mycobacterial drugs. Keywords Bacillus Calmette-Guérin, intravesical immunotherapy, mycobacteria, mycotic aneurysm Declaration of Interests No conflict of interests declared. PDF https://www.rcpe.ac.uk/sites/default/files/lambie.pdf Journal Keywords: Bacillus Calmette-Guérinintravesical immunotherapymycobacteriamycotic aneurysm