The development of the concept of anaplastic large cell lymphoma is reviewed. The subtypes of the tumor proposed in the literature, including the so-called Hodgkin's-like variant, are discussed both on morphological and clinical grounds. The more recent information on the genetic and molecular characteristics of the tumor (i.e. 2;5 translocation, formation of the NPM/ALK hybrid gene, and production of a specific protein) are presented: their possible implications in the future classification and clinical management of the neoplasm are discussed.