We discuss two cases of anaplastic lymphoma kinase (ALK)-positive lung cancer in which complex renal cysts were observed during crizotinib administration. Case 1 was a 64-year-old female, diagnosed with Stage IV pulmonary adenocarcinoma. The tumor was found by immunohistochemistry (IHC) to be ALK positive, so as a fifth-line chemotherapy, therapy was commenced using the ALK inhibitor crizotinib. This was seen to be effective in reducing the tumor, but five months after treatment commenced, bilateral complex renal cysts were found in a CT examination. Case 2 was a 62-year-old female, in whom one year after pulmonary adenocarcinoma surgery a relapse occurred as a result of metastasis to the spleen, and in IHC and fluorescence in situ hybridization using surgical specimens, ALK-positive lung cancer was diagnosed. As a second-line chemotherapy, treatment was carried out using crizotinib. From before the commencement of treatment, simple cysts had been observed in the left kidney, but in a CT examination three months after the start of crizotinib administration, they were observed to have grown in size and number. There has been interest in complex renal cysts resulting from crizotinib, but in this country, there have been almost no reports of this, so we are reporting on these two cases that we experienced at our hospital.