The molecular pathogenesis of lung cancer, especially multiple and synchronous bronchioloalveolar carcinomas (BACs), is still unknown. Here, we report two cases of multiple BACs associated with acromegaly, and discuss about the possible relationship between these two pathological condition. The first patient was a 52-year-old female with a history of Hardy's surgery for pituitary growth hormone cell adenoma 2 years earlier. The second patient was a 57-year-old female with acromegaly and obstructive sleep apnea syndrome. Both patients were non-smokers and showed a high serum level of insulin-like growth factor I (IGF-I) at the time of admission, even though the level of growth hormone had decreased. High-resolution computed tomography (HRCT) revealed multiple small nodules with pure ground-glass opacity (GGO) in both lungs of the first patient and a small nodule with pure GGO in the right lung of the second one. Partial resection for these tumors were performed under video-assisted thoracoscopic surgery. Resected lung specimens of the first case revealed one papillary adenocarcinoma, seven BACs, and 11 atypical adenomatous hyperplasias (AAHs). The second case showed two foci of BACs. Immunohistochemically, all BACs were strongly positive for IGF-IR which is a specific receptor for IGF-I, and all AAHs were also weakly positive for IGF-IR. Since IGF-I is known as a potent growth factor for normal as well as cancerous cells, it might play an important role for tumorigenesis and/or tumor progression of BACs through its interaction with and/or upregulation of IGF-IR. In addition, much attention should be paid to detect lung lesions in acromegaly with high serum level of IGF-I.