Twenty-four adult Chinese patients with de novo acute lymphoblastic leukemia (ALL) were studied for the BCR/ABL translocation using both conventional cytogenetics and fluorescence in situ hybridization (FISH). Eight (33%) patients had the translocation as shown by FISH and all were B-lineage ALL (8/19, 42%). Conventional cytogenetics revealed a t(9;22)(q34;q11) in six of them, but was either unsuccessful, or not done in the other two. Seven of the eight positive cases (88%) showed a breakpoint at the minor breakpoint cluster region (m-BCR), which was confirmed by reverse transcriptase polymerase chain reaction (RT-PCR). To conclude, the frequency of BCR/ABL translocation in Chinese patients with de novo ALL is comparable to patients in the Western hemisphere, in contrast to a previous report. The predominance of m-BCR/ABL fusion among these Chinese patients with BCR/ABL translocation is also similar to patients in the Western population. Fluorescence in situ hybridization is a sensitive, specific and relatively simple technique for demonstrating this important unfavorable prognostic marker in ALL, even in a routine service laboratory setting.