Conventional CT (10-mm thick) and helical thin-section CT (2-mm thick) high-resolution images were obtained to study the relationship between the appearance of small peripheral adenocarcinomas of the lung and pathological findings. Eleven cases in which adenocarcinomas less than 1.0 cm in diameter were resected were retrospectively reviewed. Conventional CT images revealed air spaces within pulmonary nodules in 82% of tumors, an ill-defined margin in 91%, and involvement of vessels in 91%. When these findings are observed in pulmonary nodules, thin-section CT should be used for further examination. Helical thin-section CT images showed inhomogeneous internal attenuation (91%), irregularly undulating margins (91%), and vascular involvement (100%).