Hundred and forty-one small peripheral adenocarcinomas 2 cm or less in diameter were retrospectively studied to determine the rationale of limited resection with curative intent. We used a conventional computed tomography (CT) which used 2.5 mm thick sections to examine only the main tumor during from March 1985 to May 1999 and a spiral CT which produced 2.5 mm thick sections of the entire lung field during from June 1999 to July 2003. The incidence of small peripheral adenocarcinoma significantly increased from 12.6% to 29.1%, suggesting an increase in the rate of detection with spiral CTs. During the spiral CT era, the percentage of females, pathological stage I a tumors, predominant ground-glass opacity (GGO) tumors and limited resection were significantly higher. The incidence of multiple adenocarcinomas 2 cm or less in diameter significantly increased 2.6% to 14.1%. It increases to 21.9% in small adenocarcinomas and 63.6% in predominant GGO type, when minute GGO lesion which have been followed in 5 patients by a watch and wait policy would be bronchioloalveolar carcinoma (BAC). In conclusion, a paradigm shift of the treatment for small peripheral adenocarcinoma should be warrant, because localized BAC as noninvasive cancer is not rare and often found as multiple BACs.