Crizotinib (XALKORI®), an orally administered selective ATP competitive small molecule inhibitor of the anaplastic lymphoma kinase (ALK), has been approved multinational, including in Europe, for the treatment of patients with previously treated locally advanced ALK-positive non small cell lung cancer (NSCLC). This non interventional Post-Authorization Safety Study (PASS) examines the safety and effectiveness of crizotinib among ALK-positive NSCLC patients using existing healthcare databases in Denmark, Sweden, Finland, the Netherlands and the United States. The primary objective of this study is to estimate the incidence of adverse events that were observed in crizotinib clinical trials including 1) hepatotoxicity, 2) pneumonitis/ interstitial lung disease, 3) QT interval prolongation, 4) bradycardia, and 5) vision disorder. Less frequently observed adverse events, i.e. renal cysts, edema, leukopenia, neuropathy, and photosensitivity as well as patient survival will also be examined. To contextualize the incidence of the adverse event in crizotinib treated patients, the incidence of these adverse events in patients prescribed three other orally administered tyrosine kinase inhibitors, ceritinib, erlotinib and gefitinib, will be estimated.The international classification of diseases (ICD) diagnostic codes and procedural codes will be used to capture the safety endpoints in the healthcare databases. Additionally, a validation sub study among all crizotinib patients and the same number of ceritinib, erlotinib or gefitinib patients will evaluate the accuracy of the ICD-based endpoint classifications. The validation study will compare ICD-based classification of primary endpoints to endpoints adjudicated by a panel of experts using data abstracted from patient medical records.