Diabetes mellitus has been reported to modify the presenting features of pulmonary tuberculosis, but there are varying data, particularly regarding the association with lower lung field involvement. Objectives: To determine whether diabetes mellitus alters the clinical and radiographic manifestations of tuberculosis in nonimmunocompromised hosts and to define the determinants of lower lung field involvement. Methods: A retrospective review of the records of all patients with tuberculosis and diabetes mellitus seen during a 14-year period and of an age- and sex-matched nondiabetic control group with tuberculosis was carried out. The duration of symptoms, tuberculin reaction, bacteriologic and radiographic findings of the two groups were compared. Results: The presence of diabetes mellitus was found not to have an effect on patients’ symptomatology, bacteriology results, tuberculin reaction and localization of pulmonary infiltrates. On the other hand, fewer diabetic patients were smear-positive and fewer had reticulonodular opacities compared with the control patients. A higher number of insulin-dependent diabetic patients presented with cavitary disease as compared with nondiabetic controls. Lower lung field tuberculosis was significantly associated with female gender and, in patients older than 40 years, was more frequently observed in diabetics. Conclusion: These data show that diabetes does not affect the presenting features of pulmonary tuberculosis to a large extent and is only associated with lower lung field disease in older patients.