Three cases are reported in which an initial diagnosis of the plasma cell variant of Castleman's disease was made, but in which a second lymph node biopsy within a year showed evidence of Hodgkin's disease. Review of the initial biopsy indicated that atypical CD15 and CD30 positive cells were present in the initial biopsy. This illustrates the difficulty in making the diagnosis of Castleman's disease and suggests that the lymphoid reaction to the presence of Hodgkin's disease may result in similar histological appearances. The need for re-evaluation of the diagnosis of Castleman's disease in the face of persistent or recurrent disease is stressed.