Atypical adenomatous hyperplasia (AAH) is a possible precursor lesion of adenocarcinoma of the lung, but there have been no reports of AAH focusing on autopsy studies of the lungs of elderly patients, who have higher lung cancer mortality rates. We intended to clarify the characteristics of AAH in the general elderly population on the basis of the findings in autopsy cases. A total of 19 AAH lesions were found microscopically in 16 out of 241 autopsy cases (6.6%). AAH was found in only two cases of adenocarcinoma among 28 lung cancer cases. p53 immunoreactivity was observed in one of 11 low-grade AAH lesions (9.1%), but in three of four high-grade AAH lesions (75%, P=0.03) and the cases of high-grade AAH were more frequently positive for Ki-67 and CEA than the low-grade cases and less positive for pro-surfactant apoprotein C. Four of 123 patients without malignant neoplasms (3.4%) and 12 of 118 patients with malignant neoplasms (11.1%) had AAH (P=0.03). The finding that AAH was more common in the cases with malignancy than in those without malignancy indicated that genesis of AAH may be closely associated with that of malignant neoplasms.