A highly distinctive subset of renal neoplasms of children and young adults contains a t(6;11)(p21;q12), a translocation recently been shown to result in fusion of Alpha, a gene on 11q12, with the transcription factor gene TFEB on 6p21. To define the clinicopathologic spectrum of this nascent entity and to establish immunohistochemical (IHC) and molecular methods for the detection of the specific Alpha-TFEB fusion, we studied 7 renal neoplasms that showed the t(6;11) by cytogenetic or molecular analysis (patient age: range, 9-33 years; mean, 17 years). While all tumors were confined to the kidney, 3 tumors demonstrated vascular invasion. In limited follow-up, none has metastasized. We postulated that the Alpha-TFEB gene fusion may result in deregulated expression of TFEB protein that would be detectable by IHC. Using a polyclonal antibody to TFEB on formalin-fixed, paraffin-embedded tissue sections, we found that all 7 renal neoplasms with the t(6;11) demonstrated moderate (2 cases) or strong (5 cases) nuclear TFEB immunoreactivity. In contrast, none of 1089 other tumors (of 74 histologic types from 16 sites) labeled significantly for TFEB. Nuclear immunoreactivity for TFEB in normal tissues was extremely rare, limited to weak labeling of scattered benign lymphocytes. We also show that the Alpha-TFEB fusion RNAs are highly variable in size and structure, making detection by reverse-transcriptase polymerase chain reaction (RT-PCR) less reliable than for other gene fusions. Because Alpha is an intronless gene and therefore lacks splice signals, we hypothesized that DNA PCR and RT-PCR products would be identical, allowing for the use of more robust molecular assays based on genomic DNA. Indeed, in 2 cases with available frozen tissue, we showed the genomic Alpha-TFEB junction detected by DNA PCR to be identical to the Alpha-TFEB fusion mRNA detected by RT-PCR. In summary, renal neoplasms with the t(6;11) are a distinctive neoplastic entity with many similarities to the Xp11 translocation carcinomas, and together with the latter form a growing "MiTF/TFE family" of translocation carcinomas. Nuclear immunoreactivity for TFEB protein is a highly sensitive and specific diagnostic marker for these renal neoplasms. Finally, the special molecular features of the Alpha-TFEB gene fusion allow its molecular detection by DNA PCR as a robust alternative to RT-PCR in clinical tumor samples.