To analyze the radiographic characteristics of small adenocarcinomas of the lung that can be detected by computed tomography (CT), 46 resected small peripheral adenocarcinomas measuring less than 15 mm in diameter were retrospectively reviewed, and the marginal and internal findings and surrounding vessels of the tumors as shown on thin-section CT images were correlated with six histologic classifications (types A-F) as defined by Noguchi et al. The adenocarcinoma CT images were classified into two patterns: a solid-density type (n = 21) and an air-containing type (n = 25). The lesions of the air-containing type were further divided into two different growth patterns: a complete air-containing type (n = 12) and an incomplete air-containing type (n = 13). The solid-density adenocarcinomas shown in the CT images fell mainly into the C, D, F and Noguchi classifications. Although one sample in the complete air-containing category was type C, the rest were type A. The incomplete air-containing category included 4 type As and 9 type Bs. The CT findings for the 24 adenocarcinomas in the air-containing category (96%) showed an opaque ground-glass internal texture. Plural vascular involvement was observed in all 46 adenocarcinomas examined. Our results suggest that thin-section CT findings can play an important role in differentiating lung cancer and increasing our knowledge of the radiologic and pathologic correlations.