Sputum smear and culture conversion are important indicators for the effectiveness of treatment and the infectivity of the patient. The aim of this study was to identify the factors influencing both sputum smear and culture conversion time among patients with new case pulmonary tuberculosis (TB). The study was conducted in a reference hospital in Turkey in which 737 patients with pulmonary TB were hospitalised between January 2000 and 2005. We evaluated 306 (193 men and 113 women) human immunodeficiency virus-negative patients diagnosed with new case pulmonary TB. Factors associated with both sputum smear and culture conversion time (days) were investigated. Patients with diabetes mellitus (DM), cavitary disease, radiologically extensive disease had longer sputum smear and culture conversion time than the other groups. In addition, old age, male sex, smoking and thrombocytosis were found to be significantly associated with sputum smear conversion time. In the logistic regression analysis, the presence of DM and extensive disease were determined as independent factors associated with persistent sputum smear and culture positivity at the end of 2 months. The presence of DM and extensive disease were found to be independent risk factors influencing both sputum smear and culture conversion time in pulmonary TB. Sputum smear and culture examinations should be considered together to assess the poor prognosis.