Patients with non-small cell lung cancer (NSCLC) who harbor anaplastic lymphoma kinase (ALK) gene rearrangements can derive significant clinical benefit from ALK tyrosine kinase inhibitor. Accurate patient identification is absolutely crucial for successful using ALK inhibitor treatment. However, lung cancer patients with ALK gene rearrangement after ALK inhibitor therapy eventually develop acquired resistance to treatment. In this review, the authors summarize the clinicopathologic features of ALK-rearranged NSCLC and the pros and cons of current diagnostic testing. In addition, we discuss the current diagnostic flow of ALK testing and consideration of rebiopsy sample during disease progression in patients treated by ALK inhibitors.