We observed in the same patient the development of a tonsil mucosa-associated lymphoid tissue-type lymphoma in 1994, a mediastinal Hodgkin's disease in 1998, and a colonic CD30+ anaplastic diffuse large B-cell lymphoma in 2000. A same-sized FR3-JH fragment was demonstrated by polymerase chain reaction, both at the level of total DNA and of single micromanipulated cells, showing monocytoid, Reed-Sternberg, or anaplastic morphology. Moreover, an identical IgH nucleotide sequence was detected in mucosa-associated lymphoid tissue-type lymphoma and colonic CD30+ anaplastic diffuse large B-cell lymphoma, whereas mediastinal Hodgkin's disease IgH rearrangement involved different VH and JH genes. CD30+ Reed-Sternberg and diffuse large B-cell lymphoma cells contained Epstein-Barr virus EBER sequences that were not observed at the level of mucosa-associated lymphoid tissue-type lymphoma. Therefore, Epstein-Barr virus infection may have played a role in diffuse large B-cell lymphoma transformation of mucosa-associated lymphoid tissue-type lymphoma and in the lymphomagenesis of Hodgkin's disease. In addition to their different clonal origin, Reed-Sternberg cells of Hodgkin's disease expressed a CD15+, CD20+ (rare cells), CD30+, Oct-2-, EBNA2-, LMP1+ phenotype, whereas anaplastic and Reed-Sternberg-like cells of diffuse large B-cell lymphoma were CD15-, CD20+, CD30+, Oct-2+, EBNA2+, and LMP1+. Interestingly, we also detected scattered CD30+ Epstein-Barr virus- large cells with prominent nucleoli in the initial tonsil mucosa-associated lymphoid tissue-type lymphoma, suggesting that these cells could be prone to Epstein-Barr virus infection and/or large cell transformation.