The project to finalize a 'closed loop' insulin delivery according to blood glucose level, i.e. an implanted artificial beta cell, is born from the development of the first miniaturized portable insulin pumps during the 1970s. Continuous improvements in micro-electronics, as well as in the development of biomaterials and stable insulin solutions, have led to the availability of implantable pumps able to infuse insulin by the peritoneal route, in a continuous and programmable way, for several years. These systems represent the most efficient and physiological mode of insulin therapy at the present time. More recently, we have demonstrated during clinical trials that intravascular, implantable, glucose sensors using glucose-oxidase were able to measure with good accuracy real-time blood glucose for several months. The combination of these two devices to form a prototype of implantable artificial beta cell, designated as Long Term Sensor System, allowed us to perform the first trials of closed-loop insulin delivery according to sensor signal for periods of 48 hours in type 1 diabetic patients. This mode of functioning appeared to be feasible and able to establish glucose control closer to physiology than the use of implantable pumps in open-loop, i.e. by adapting insulin delivery according to capillary blood glucose. Although algorithms tuning automated insulin delivery are improvable, the success of these initial trials materializes the perspective of a possible restoration of physiological insulin function by the mean of an implanted artificial beta cell in diabetic patients.