A histopathological reexamination was made of diagnostic material in 223 patients with Hodgkin's disease (HD) collected between 1971 and 1981. The diagnosis of HD was considered to be incorrect in 90 cases (40%). Change of diagnosis to non-Hodgkin's lymphoma was made in 56 cases, of which 23 were high-grade and 26 were low-grade lymphomas (7 not determined), and to angioimmunoblastic lymphadenopathy in 10 cases. These discrepancies were considered to be due mainly to progress in the understanding and classification of malignant lymphomas, which stresses the importance of review of histologic material in retrospective studies on Hodgkin's disease.