We report the case of a patient, who suffered from an acute BCG-pneumonitis after the fourth treatment of his bladder cancer with intravesical instillation of BCG. The chest-x-ray presented a bilateral reticulonodular infiltration. Mycobacterium tuberculosis could not be detected by culture, biopsy or PCR assay. Under treatment with Rifampicine, Isoniazid and Ethambutol the patient recovered within a short time and the follow up chest-x-ray became normal. A supplementary steroid therapy was not needed.