The purpose of this study was to evaluate the contrast-enhanced CT characteristics of pathologic thoraco-abdominal lymph nodes in 38 patients infected with Mycobacterium tuberculosis (30 without AIDS and eight with AIDS). Unenhanced scans of chest, abdomen and pelvis were also done in all cases. The CT attenuation values and the enhancement characteristics of the largest node or group of lymph nodes were evaluated in a dynamic sequence over a period of 10 min. On unenhanced CT the nodes were of low attenuation (less than 30 HU) in 18 cases and of soft tissue attenuation (greater than 35 HU) in 20 cases. Four post-contrast patterns of enhancement were found: (i) peripheral rim enhancement (n = 22); (ii) inhomogeneous enhancement (n = 8); (iii) homogeneous enhancement (n = 6); and (iv) homogeneous nonenhancing nodes (n = 2). Increase of attenuation and obliteration of perinodal fat was found in 13 cases, most of them with the peripheral rim enhancement pattern. Seven cases had a combination of enhancing patterns in the same nodal group. The central enhancement was usually moderate (mean, 30 HU) but was marked (greater than 60 HU) in three patients with the homogeneous enhancement pattern. Neither the nodal attenuation values nor the patterns of enhancement are characteristic of tuberculosis, however adenopathy showing peripheral rim-enhancement with relative low attenuation centres can suggest a diagnosis of tuberculosis in the appropriate clinical setting.