Telomere-dependent replicative senescence is one of the mechanisms that limit the number of population doublings of normal human cells. By overexpression of telomerase cells of various origins have been successfully immortalized without changing the phenotype. While only a limited number of telomerase immortalized cells of epithelial origin are available, none of renal origin has been reported so far. Here we have established simple and safe conditions that allow serial passaging of renal proximal tubular epithelial cells until entry into telomere-dependent replicative senescence. As reported for other cells, senescence of renal proximal tubular epithelial cells is characterized by arrest in G1 phase, shortened telomeres, staining for senescence-associated -galactosidase, and accumulation of -H2AX foci. Furthermore, ectopic expression of the catalytic subunit of telomerase was sufficient to immortalize these cells. Characterization of immortalized RPTEC/TERT1 show characteristic morphological and functional properties like formation of tight junctions and domes, expression of aminopeptidase N, cAMP induction by para-thyroid hormone, sodium-dependent phosphate uptake and the megalin/cubilin transport system. No genomic instability within up to 90 population doublings has been observed. Therefore, these cells are proposed as a valuable model system not only for cell biology, but also for toxicology, drug screening, biogerontology as well as tissue engineering approaches.