The vaccine strain Mycobacterium bovis BCG may lead to disseminated infection in patients with immune deficiency In this report a patient who developed fatal disseminated tuberculosis caused by M bovis BCG strain was presented One year old male patient with the previous history of recurrent lower respiratory tract infection, was admitted to the hospital with the complaints of fever, cough and diarrhea continuing for 20 days There was no family history of tuberculosis or history of contact with a tuberculosis case. Physical examination of the case revealed growth retardation and reticular and reticulonodular infiltration was detected in his chest X-ray. The results of sweat test, cystic fibrosis gene mutation analysis and metabolic screening tests were normal. Since fever continued and infiltrations persisted in the chest X-ray despite antibiotic therapy, PPD test was applied and acid-fast bacilli (AFB) were investigated in his gastric aspirate and stool samples for three consecutive days. PPD test was negative and no AFB were detected in the microscopic examination of the clinical samples. However, growth in Lowenstein-Jensen medium was detected in the stool sample on the 38(th) day of incubation. The antimycobacterial susceptibility testing performed at BACTEC MGIT (Mycobacterial Growth Indicator Tube) 960 system (Becton-Dickinson, USA) revealed that the isolate was susceptible to rifampin, isoniazid, streptomicin and ethambutol Since the isolates did not grow at PNB (para-nitro benzoic acid) medium and niacin and nitrate activities were negative, spoligotyping (spacer oligonucleotide typing) was performed and DR loci characteristic for M bovis BCG strain were detected. However, the patient died 2 weeks before the culture results were obtained The effective use of mycobacteriology laboratories and cooperation between laboratory and clinics provide advantages in the early diagnosis and treatment of tuberculosis cases, decreasing the morbidity and the mortality.