The ETV6 gene is rearranged as a result of translocations involving a wide variety of chromosomal partners. To date, 12 partner genes for ETV6 have been cloned, and a further 23 chromosomal regions have been described. We previously identified a cryptic t(7;12) with ETV6 involvement in two cases of infant leukemia. The finding of a third case of t(7;12), also in an infant, prompted a more focussed search based on the common features found in these patients and those reported in the literature. The selection criteria were age at diagnosis < 20 months and the presence of +19 and/or +8 in the karyotype; cases with abnormalities of 7q and/or 12p were also considered. FISH studies using whole chromosome paints and probes for the ETV6 gene revealed a t(7;12) in 10 out of 23 cases studied. Seven of these had evidence of ETV6 rearrangement. Of those with ETV6 involvement, six had a 7q36 and one a 7q22 breakpoint. Importantly, in three cases the 7q36 breakpoint was within the same PAC, suggesting the existence of a new nonrandom translocation. However, in at least one patient the 7q36 breakpoint was different. The identification of the 7q partner genes will determine whether it is the disruption of ETV6 alone, or the formation of fusion genes, that is important for leukemogenesis in these patients. As both 7q36 and 7q22 are critical regions of gene loss in del(7q) leukemias, the identification of partner genes from these regions may also be important in understanding the pathogenesis of these diseases.