A 60-year-old man with a history of smoking was transferred to our hospital for consciousness disorder. A diagnosis of ALK-rearranged lung adenocarcinoma associated with a paraneoplastic electrolytic disorder was made following a cutaneous needle biopsy. Both the primary lung lesion and multiple metastases shrunk and his electrolytic disorder resolved after the introduction of a first-line molecular-targeted drug chemotherapy with crizotinib. We herein report a case of ALK-rearranged lung adenocarcinoma accompanied by SIADH, successfully treated with crizotinib.