OBJECTIVE Diagnosis of tuberculosis and/or mycobacteria infection is particularly difficult in immunocompromised patients. METHODS We examined the clinical presentation, means of diagnosis, treatment and outcome of tuberculosis in a retrospective study of 6 patients among 75 with hairy cell leukemia diagnosed from 1982 to 1995. RESULTS Hearlding symptoms of tuberculosis diagnosis were: fever (6/6), weight loss (4/6), pleural effusion (1/6), superficial adenopathy (1/6), persistence of cytopenia or splenomegaly during the treatment of hairy cell leukemia. Pulmonary symptoms were present in only two cases. Diagnosis was obtained by positive culture of mycobacteria in 2 cases (Mycobacterium tuberculosis in pleural effusion, Mycobacterium kansaii in adenopathy). Microbiological diagnosis was never obtained from sputum (6/6). Diagnosis was obtained by histopathology in all cases: from bone marrow (2 cases), lymph nodes (2 cases), liver (1 case), spleen (1 case), umbilical fat (1 case). Tuberculosis was disseminated in all cases. By clinical, biological, microbiological histopathological means and response to treatment, tuberculosis was considered as: hematopoietic in all cases, hepatic (in 4/6), pleural (1/6), pulmonary (1/6). A favorable outcome of tuberculosis was observed in all cases. No death was observed. CONCLUSIONS Tuberculosis was found in 8% of hair cell leukemia patients. In hairy cell leukemia, tuberculosis is characterized by few pulmonary symptoms and scarse microbiological documentation. In contrast, histopathology is very interesting to confirm diagnosis. Tuberculosis is in most cases disseminated and in particular hematopoietic diffusions is always present. In spite of existensive localization, the prognosis remains excellent and all patients can be cured. In our opinion, this good prognosis may be linked to the improvement of hairy cell leukemia treatment observed since the advent of interferon pentostatin and 2cdA.