To see the usefulness of CT in evaluation of response to treatment in patients with mediastinal tuberculous lymphadenitis (MTL), we analyzed the initial CT patterns and follow-up CTs or serial plain radiographs during 18 months antituberculous chemotheraphy in 58 consecutive patients. CT patterns of MTL at the beginning of treatment were categorized into solid type (n=8), low density with peripheral rim enhancement type (n=36), extranodal extension type (n=9) and calcified type (n=5). According to the response to treatment, each patient was categorized into prompt response group (response after three months but residual lesion after one year), no response group (no change in size during 18 months treatment) and temporal increase group (temporal increase in size during the treatment but ultimately improved with chemotheraphy) Among 29 cases of prompt response group, 20 cases had large low-density areas. 6 cases had diffuse or extensive node involvement with extranodal extension or tracheal compression. Two patients with acquired immune deifciency syndrome belonged to this group. Fifteen cases of slow response group had low-density nedes in 7 patients and small solid or extranodal-extension or tracheal compression. Two patients with acquired immune deifciency syndrome belonged to this group. Fifteen cases of slow response group had low-density nedes in 7 patients and small solid or extranodal-extension nodes in 6 patents. They were associated with disseminated pulmonary tuberculosis, generalized lymphadenopathy or other organ (pericardium, brain, bone, or abdomen) involvement. In 5 cases of no response group, there were 3 cases of calcified node and 2 cases of small soild nodes. Nine cases of temporal increase group included low density type of MTL only. And they were associated with disseminated pulmonary of endobronchial tuberculosis. In conclusion, response to antituberculous chemotherapy could be predicted in patients with MTL on the basis of CT findings before treatment