Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase protein implicated in a variety of tumors, both solid and hematological. Few years ago crizotinib, an inhibitor of the receptor tyrosine kinases c-Met and ALK, demonstrated its activity in ALK positive non-small-cell lung cancer and other tumors with excellent toxicity profile. Subsequently several ALK inhibitors have been developed, offering new personalized treatment options. This review addresses some clinical considerations on the use of ALK inhibitors in ALK positive tumors and on the development of resistance to them.