The cnidarian Hydra polyps escape senescence, most likely due to the robust activity of their three stem cell populations. These stem cells continuously self-renew in the body column and differentiate at the extremities following a tightly coordinated spatial pattern. Paul Brien showed in 1953 that in one particular species Hydra oligactis cold-dependent sexual differentiation leads to rapid aging and death. Here we review the features of this inducible aging phenotype. These cellular alterations, detected after several weeks after aging was induced, are characterized by decreasing density of somatic interstitial cell derivatives, disorganization of the apical nervous system and disorganization of the epithelial cells myofibers. Consequently, tissue replacement required to maintain homeostasis, feeding behavior, and contractility of the animal are dramatically affected. Interestingly, this aging phenotype is not observed in all H. oligactis strains, thus providing a powerful experimental model for investigations on the genetic control of aging. Given the presence in the cnidarian genome of a large number of human orthologs that were lost in ecdysozoans, such approaches might help uncover novel regulators of aging in vertebrates.