Although cytogenetic data suggest that the t(2;5)-(p23;q35) translocation occurs in many cases of CD30+ lymphomas, the exact frequency of this event is still unknown. To clarify this issue and its epidemiological characteristics, we examined 37 formalin-fixed, paraffin-embedded specimens of CD30+ lymphomas from the United States and Hong Kong by reverse transcriptase-polymerase chain reaction (RT-PCR) for the status of the NPM and ALK genes, which are typically juxtaposed by the t(2;5) translocation. Thirty-four cases were classified as anaplastic large cell lymphomas (ALCL), 2 cases as non-anaplastic large cell lymphomas (LCL), and 1 case as the small cell variant of CD30+ lymphoma. The t(2;5) translocation was detected in 6 cases (16%), including 3 of 18 American patients and 3 of 19 cases from Hong Kong. All cases had a 185-bp NPM RT-PCR product as detected by Southern blot analysis, indicating adequate preservation of mRNA. The 6 positive cases were among 4 of 34 adult lymphomas, as compared with 2 of 3 childhood cases. Five of 17 T-lineage cases were t(2;5)-positive, compared with 1 of 15 B-lineage cases and none of the 5 null-cell or mixed lineage cases. Our results therefore show that t(2;5) occurs at a low frequency among CD30+ lymphomas, at least in our adult-dominated series.