Apo2L/TRAIL is a member of the TNF family, with its receptors DR4 and DR5 containing a death domain. Multiple tumors are sensitive to Apo2L/TRAIL-induced apoptosis, while normal cells are not, so it constitutes a promising new antitumoral therapy. In this review we deal rather with the physiological role of Apo2L/TRAIL, which, in one hand, is clearly related with immune antitumoral surveillance. However, a role of Apo2L/TRAIL as a fine-tuning regulator of the immune system, especially in the regulation of CD8⁺ T cell activation and memory, has been also demonstrated. In fact, Apo2L/TRAIL can be considered as an additional mechanism needed to prevent the development of autoimmune disease. Indeed, recent developments indicate that Apo2L/TRAIL can be also useful as a treatment against certain chronic autoimmune diseases.