A woman with Down's syndrome (DS) had subfebrile temperature, nodular/patchy shadows on the chest X-ray over the right pulmonary base, and a history of recurrent respiratory infections. She was pale, asthenic, uncommunicative, mildly anemic and the erythrocyte sedimentation rate was 80/first hour. The tuberculin skin test (TST) PPD 3 was negative. Mycobacterium tuberculosis was isolated from oral mucosal brushing, sensitive to the first line anti-tuberculosis drugs. Patients with DS and other mental disabilities need special care and attention during diagnostic procedures for tuberculosis (TB).