In 62 consecutive resections for adenocarcinoma of the lung, 50 cases (81%) had single adenocarcinomas and 12 (19%) had multiple adenocarcinomas. In seven of these 12 patients, two adenocarcinomas were found. In the other five patients, the specimen contained a dominant adenocarcinoma and several 0.1- to 1-cm nodules of similar histologic appearance. In four of the 50 single tumor patients and one of seven double tumor patients, 1- to 2-mm nodules were found along with adenocarcinomas that we interpreted as being bronchioloalveolar tumors of uncertain malignant potential. An analogy is drawn between these four types of findings and single tumors of the colon, double tumors of the colon, polyposis syndromes, and tubular adenomas of the colon, respectively.