BCG (Bacillus Calmette-Guerin) comprises an attenuated strain of Mycobacterium bovis and is used for vaccination against tuberculosis. An additional use of BCG is for immunotherapy of cancer in which the vaccine is administered intravesically for the treatment of superficial bladder cancer. The efficacy of immunotherapy with BCG in the prevention of recurrence is estimated at 70–99%, which is higher than for local chemotherapy. The most frequent complications of such treatment include fever and urinary bladder inflammation, while serious complications of haematogenous organ inflammation, especially inflammation of the lungs with the formation of pulmonary caseosus granulomas, are rarely seen. The authors reported a case of a 68-year-old man who was treated with intravesical BCG instillations due to a superficial bladder cancer. The patient underwent transurethral resection of bladder cancer and then periodically received intravesical BCG instillations. A few days after one instillation, systemic symptoms with a high fever appeared. Further examinations showed features of hepatitis and spread pulmonary changes. The patient underwent videothoracoscopy, and a fragment of lung parenchyma was collected. The histopathological examination revealed the presence of granulomas with central caseosus necrosis. Suspecting BCG infection, diagnostics were enhanced to include bacteriological and genetic tests for the presence of acid-resistant bacilli, which finally gave negative results. The authors diagnosed granulomatous pneumonia as a complication of intravesical BCG immunotherapy. Treatment with antituberculous drugs was initiated. After completing pharmacological treatment, radiological control was performed, which showed significant but not complete remission of pulmonary changes.