A 65-year-old patient without specific associated pathology was treated for a high-grade non-invasive papillary urothelial carcinoma by surgery associated with repeated intravesical Bacillus Calmette-Guérin (BCG) instillations. During follow-up, magnetic resonance imaging (MRI) found a clinically indurated prostate nodule with suspected extensive capsular invasion. Prostatic biopsies showed epithelioid and giant-cell granuloma associated with a single focus of adenocarcinoma. Urinary culture test and specific PCR confirmed the involvement of Mycobacterium bovis. The patient was treated first by rifampin, isoniazid and ethambutol and then by rifampin and isoniazid for a total duration of 9 months, with MRI reassessment at various intervals. After BCG therapy, systemic infectious complications but also local complications such as granulomatous disease have been reported, but prostatic abscesses with M. bovis mimicking cancer on MRI are rare. Consequently, we advise specific local urinary and prostate samples to test for mycobacteria (staining, culture, PCR) in order to avoid aggressive high-risk prostatic surgery.