To study the frequency of a factor of immunodepression in patients with tuberculosis, the differences in presentation, and the diagnosis and therapeutic management according to the immune status. Retrospective study of the files of patients hospitalised in the University Hospital Centre of Rennes in 1998 for a Mycobacterium tuberculosis infection. Comparison of two populations, immunodepressed versus non immunodepressed. 75 patients aged 20 to 91 were included, 41 patients were considered immunodepressed and 34 non immunodepressed. The causes of immunodepression were: HIV infection (n = 2), diabetes (n = 4), chronic alcoholism (n = 12), chronic respiratory diseases treated with corticosteroids (n = 6), neoplasia (n = 9), and inflammatory diseases (n = 7). Comparison between the 2 populations revealed more a frequent history of tuberculosis in the immunodepressed (p = 0.04), shorter delay before diagnosis (p = 0.04), greater frequency of disseminated forms (p = 0.02) and enhanced mortality (p = 0.01). There was no difference in the 2 groups with regard to the clinical signs having evoked tuberculosis, the diagnostic method, the bacteriological results or the modalities of treatment. The frequent reactivation of tuberculosis in immunodepressed patients and the severity of the infection in these patients should evoke tuberculosis and the rapid initiation of an efficient treatment in such patients. In the case of alteration in immune defences, prophylactic treatment should help to reduce the number of such reactivations.