The TERT (telomerase reverse transcriptase, a.k.a. EST2, TCS1) gene encodes the reverse transcriptase component, a catalytic domain of the enzyme telomerase. Telomerases are necessary to maintain the ends of chromosomes and are inactive in the majority of somatic cells but active in cancer cells. Remodeling of the genomic context, due to 5p15.33 rearrangements, abrogates transcriptional silencing of the TERT gene. TERT translocations are the second common aberration found in neuroblastomas. These translocations are observed either in a 50 kb region proximal or more rarely in a 40 kb region distal to the gene. Molecular genetic studies showed that rearrangements of the chromosomal region 5p15.33 occur exclusively in high-risk neuroblastomas. Therefore, TERT rearrangements are considered to define a sub-group of high-risk neuroblastomas with a poor prognosis. Rearrangements of TERT are found in chromophobe renal cell carcinomas, non-Hodgkin lymphomas, and mantle cell lymphomas. FISH is a suitable tool for the detection of these TERT rearrangements and thus may be of prognostic relevance.