A 23-year old woman was admitted to our hospital with hemoptysis. The chest X-ray showed reticulonodular opacity and multiple cysts throughout the entire lung field. The chest CT scan revealed numerous bilateral cysts with various sizes, some of them with thickened walls. An open lung wedge resection was performed. The resected specimen showed scattered small nodules, 0.3 to 0.6 cm in size. Microscopically, each nodule was composed of atypical glands with an occasional papillary architecture spreading to the alveolar septa, which were morphologically consistent with a papillary adenocarcinoma with a bronchioloalveolar carcinoma growth pattern. Immunochemically, the tumor cells were negative for the S-100 protein. The patient was diagnosed with an adenocarcinoma of the lung. A variety of diseases can produce or mimic multiple, thin-walled cysts in the lung. Lung cancer with multiple cysts is quite rare. Nevertheless, adenocarcinoma should be a diagnostic consideration. We report a case of a multiple cystic adenocarcinoma of the lung.