Some anaplastic large cell lymphomas (ALCLs) carry a specific chromosomal translocation, t(2;5)(p23;q35). Recently, we found a novel hyperphosphorylated 80-kDa protein tyrosine kinase, p80, in ALCLs with t(2;5). Subsequent cDNA cloning revealed p80 to be a fusion protein of two genes, the novel tyrosine kinase gene and the nucleophosmin gene, in accordance with the sequence of the NPM/ALK gene (Morris et al.). Meanwhile, the clinicopathologic features of p80-carrying ALCLs have remained unclear. Paraffin sections of 105 cases of ALCL were immunostained using anti-p80 antibody, and 30 of them were shown to express p80. Clinicopathological comparison between p80-positive and -negative ALCLs revealed that p80-positive cases occurred in a far younger patient age group and the patients showed a far better 5-year survival rate. These data showed that p80-positive ALCL is a distinct entity both clinically and pathogenetically, and should be differentiated from p80-negative ALCL.