In a series of 247 consecutive resections for lung carcinoma, 23 (9.3%) patients had a total of 41 incidentally found nodules measuring 1-7 mm in diameter. These lesions were characterized histologically by lepidic growth and variable cellular atypia; they were interpreted as bronchioloalveolar adenomas. Five additional patients had dozens of such nodules in addition to their dominant tumor. One of these patients had this process bilaterally. It appears that these adenomas are an early, premalignant phase of glandular neoplasia with a potential for evolution to carcinoma. This phenomenon may help explain the relatively high incidence of multicentric synchronous and metachronous lung cancer cited in the literature.