The incidence of pulmonary tuberculosis in Japan has decreased remarkably. However, high frequency of tuberculosis can still be noticed in those subjects with underlying diseases, the so-called compromised host. This study aimed at to clarify the clinical characteristics of pulmonary tuberculosis in the compromised host. To achieve our objective we compare the clinical and radiological findings in patients with and without underlying disease. This study comprised 44 pulmonary tuberculosis patients. Among these, 24 cases (55%) of tuberculosis occurred in those with a pre-existing disease. Most patients of the compromised host group were seen because of pulmonary symptomatology. There were 3 cases (15%) with cavitated pulmonary infiltration in the normal host group, whereas in the compromised host group 7 cases (29%) presented cavitary lesions. From these results, it was confirmed the high frequency of pulmonary tuberculosis in patients with an underlying disease. In addition, this work suggests that the presence of an atypical radiological findings should orient the clinician to start an early work-up for the diagnosis of pulmonary tuberculosis in those high risk group of patients.