A 71-year-old woman with synchronous bilateral primary lung carcinomas accompanied by multiple atypical adenomatous hyperplasias is described. The patient was found to have bilateral tumors during preoperative workup for the previously detected well differentiated adenocarcinoma of the right lung. Thoracoscopic wedge resection of the left upper lobe was performed to obtain a definitive diagnosis of the left lesion. Although intraoperative diagnosis was made by frozen section as atypical papillary lesion, postoperative diagnosis of this lesion was changed to well differentiated adenocarcinoma accompanied by surrounding atypical adenomatous hyperplasia (AAH). We diagnosed that the bilateral lesions were synchronous primary well differentiated adenocarcinomas independent to each other based on the criteria of Martini and Melamed and performed right upper and mediastinal lymph node dissection. The resected lobe contained not only the primary adenocarcinoma but also multiple small gray nodules which were diagnosed as AAHs. In summary, it was diagnosed that the patient had synchronous double primary lung adenocarcinomas of T1 N0 M0 pathological stage and 12 solitary atypical adenomatous hyperplasias. The patient is doing well with no signs of recurrence 24 months after the operation. This case might be an example of the adenoma-carcinoma sequence of lung cancer. A careful follow-up study is mandatory for this patient with special regard to the further development of lung carcinoma in the future.