We studied nosocomial infections due to Mycobacterium bovis bacille Calmette-Guérin (BCG) Onco-TICE bacteria, transmitted by contamination of medication prepared in BCG Onco-TICE-contaminated hoods in the pharmacy, in 5 immunocompromised patients at 3 hospitals. The BCG strains cultured from the patients had the same DNA profile as the BCG Onco-TICE strain used for bladder instillation. To prevent these infections, a change from open to closed preparation was made; strictly separated preparation in time of BCG Onco-TICE instillation and chemotherapy was enforced, the biological safety cabinet was disinfected between preparations, and gloves were changed between preparations.