Small cell carcinoma of the lung is different from non-small cell carcinoma of the lung in many respects such as its tendency toward earlier distant metastasis and principles of treatment. Although radiological findings of small cell carcinoma of the lung are well known including CT and many articles are published about the bronchogenic carcinoma and criteria of mediastinal lymph node metastasis by its size. None of them deals with the possibilities of differentiating small cell carcinoma and non-small cell carcinoma of the lung by the morphologic characteristics of metastasized mediastinal lymph nodes. We analyzed retrospectively CT scans of 31 patients with pathologically proven bron-chogenic carcinoma of the lung who had mediastinal lymph node metastasis with special attention to the possibilities of differentiating small cell carcinoma from non-small cell carcino-ma by the morphologic characteristics of lymph nodes. 11 of the 31 patients were small cell carcinoma of the lung and 20 patients were non-small cell carcinoma including 17 cases of squamous cell carcinoma 1 cases of adenocarcinoma large cell undifferentiated carcinoma and bronchioloalveolar cell carcinoma respectively. Mediastinal lymph nodes in small cell carcinomas tends to be larger in size (over 2cm in two-thirds of patients) than non-small cell carcinoma. mean number of the involved lymph nodes in small cell carcinoma are twice as many as that of non-small cell carcinoma High incidence of central low density of involved lymph node was found in both small cell carcinoma(80.5%) and non-small cell carcinoma(77.5%) but homogeneous central low density is more frequent in small cell carcinoma(50%) than non-small cell carcinoma(23.6%) High incidence of peripheral rim enhancement of involved lumph nodes was found both in small cell carcinoma(79.0%) and non-small cell carcinoma(87.3%) there was no difference between small cell carcinoma and non-small cell carcinoma in respect to involved nodal groups.