Fatal disseminated mycobacterial infection following intravesical bacillus Calmette-Guerin. We describe a fatal case of disseminated mycobacteriosis after intravesical bacillus Calmette-Guerin immunotherapy. We summarize the prior safety record of this therapeutic modality, discuss local and systemic pathophysiological mechanisms by which dissemination might have occurred, and review the reported clinical experience with antituberculous chemotherapy for significant bacillus Calmette-Guerin infection. Finally, we offer suggestions for prophylaxis of certain patients with a history of exposure to intravesical bacillus Calmette-Guerin. 