BACKGROUND: To analyze the morphologic characteristics of low density lymph node in etiologic differentiation of lymphadenopathy, emphasizing the different features between tuberculosis and lung cancer, on contrast enhanced CT scan,. METHOD: A total of 64 patients who showed low density lymph nodes on chest CT scan were analyzed. Primary causes were tuberculosis (n=28), lung cancer (n=27), malignant lymphoma (n=5) and metastasis from extrathoracic malignancies (n = 4). CT scan was performed with 10mm slice thickness and 7 characteristic features were evaluated: location,size, presence or absence of the nonnecrotic lymph node, calcification, perinodal fat obliteration, thickness and evenness of the enhancing rim. RESULTS: In patients with tuberculous lymphadenopathy, lymph nodes with uneven (68.0%) and thick (62.1%) enhancing rim were more common than lung cancer (p<0.05). Low density lymph nodes with less than 1cm in size were found only in tuberculous lymphadenopathy(n=10). In 48.2% of patients with lung cancer, more than 1 nonnecrotic enlarged lymph node were coexisted, whereas 21.4% in patients with tuberculous lymphadenopathy(p=0.06). However, the size, location and calcification were not statistically significant between tuberculous lymphadenopathy and lung cancer. CONCLUSION: Tuberculous lymphadenopathy is strongly suggested when enhancing rim of enlarged lymph nodes is uneven and thick, when the coexisting nonnecrotic lymph nodes are few in number and when central low density is encountered in normal sized lymph nodes.