Intravesical instillation of bacillus Calmette-Guérin (BCG) an attenuated live strain of Mycobacterium bovis , has been used in the treatment of superficial urothelial carcinoma of the bladder. Although well tolerated, it can cause local and systemic complications. We report the case of an adult male treated for carcinoma in situof the bladder with this immunotherapy, who presented, one year later, with fever and progressive pancytopenia. After an extensive workup, the bone marrow biopsy showed non-caseating granulomas and cultures grewMycobacterium bovis . He had a favorable response to the standard therapy for M. bovis infection. Disseminated BCG infection is a rare complication and often implies a challenging diagnostic workup. This case highlights the importance of early recognition of this serious complication in patients with BCG exposure for proper treatment.