Hodgkin's disease (HD) is reported in a killer whale (Orcinus orca). Generalized lymphadenopathy and splenomegaly were noted at necropsy and histopathological examination revealed diffuse proliferation of atypical large cells with huge eosinophilic nucleoli. They were often multinucleated, and binucleated forms characteristic of Sternberg-Reed cells of human HD were occasionally present. There was no cytological atypia in the background lymphocytes. Thus, the lesion was identified as analogous to HD in man. To our knowledge, this is the first recorded case of HD in the killer whale.