The haematological side effects of antitubercular drugs are not well known. We report the observation of a patient who received Rifater for the treatment of pulmonary tuberculosis. After one month of treatment, he developed an acute pulmonary infection, with neutropenia (1218/microl) and thrombocytopenia (109,000/microl), requiring suspension of his antitubercular drugs. After the reintroduction of he again developed thrombocytopenia (6,000/microl) associated with bleeding and required treatment with intravenous immunoglobulin. The introduction of a combination of moxifloxacin, isoniazid, pyrazinamide, and ethambutol was followed by a new relapse of the thrombocytopenia. Responsibility of pyrazinamide was then suspected and later confirmed by the evolution of platelet levels after stopping and reintroducing this antibiotic. This is the third reported case of pyrazinamide induced thrombocytopenia, whose frequency is probably underestimated because of the use of compound treatment.