In this report we analyze the morphological and immunohistochemical findings observed in 5 cases of CD30/Ki-1 positive anaplastic large cell lymphoma, a recently recognized neoplastic entity. In comparison with the Ki-1 lymphomas so far described, these cases showed a fairly large number of Reed-Sternberg-like cells, often admixed with small lymphocytes and occasional eosinophils. Moreover, in all our cases immunohistochemical reactions detected the CD15/Leu-M1 antigen, together with markers of the T-lineage and of lymphoid activation. In previous studies the CD15/Leu-M1 antigen has been found in the majority of cases of Hodgkin's disease, but has been stated to be absent typically in Ki-1 lymphomas. Our results indicate that this antigen cannot be considered a reliable tool to distinguish between Ki-1 lymphomas and Hodgkin's disease. Furthermore, the morphological and immunohistochemical findings reported suggest that in some cases Ki-1 cell lymphoma and Hodgkin's disease may be closely related. They may represent different steps in the progression of the same lymphoproliferative disorder.