The current classification of lymphoid neoplasms is based on the integrated utilisation of morphological, immunohistochemical, genetic and clinical criteria to define disease entities. Anaplastic large cell lymphoma is a paradigm for the identification of a disease entity based on morphological observations and immunophenotype, which paved the way for the subsequent discovery of the characteristic cytogenetic abnormality the translocation t(2;5)(p23;q35). In 1994, the t(2;5) was cloned and the NPM-ALK fusion gene generated by this rearrangement was identified. The year 2014 marked the 20th anniversary of this seminal publication by Steve Morris et al. The discovery of anaplastic lymphoma kinase (ALK) has allowed the definition of a distinct entity within the clinically and pathologically heterogeneous group of CD30+ lymphomas. The diagnosis of ALK-positive ALCL has become straightforward due to the generation of the reliable monoclonal antibody ALK-1 that also has led to the recognition of the histologic spectrum of the disease. ALK-positive ALCL has evolved in the last 20 years to an exciting model for signal transduction studies and targeted therapy.