Bacillus Calmette-Guerin (BCG) therapy for treatment of bladder cancer is a rare cause of Mycobacterium bovis infected aortic aneurysm. Typical presentations have included general malaise, fever, and lower back pain. We present a case with lower back pain and constipation as presenting symptoms, leading to diagnosis of mycotic aneurysm presumed secondary to intravesical BCG therapy. Treatment included open surgical repair with femoral vein grafting and anti-tubercular therapy. This case highlights the importance of a high index of suspicion for less common infectious complications of BCG therapy.