The management of patients with peripheral arterial disease (PAD) stage IIb and pain-free walking distance (PFWD) less than 100 meters is a major clinical problem, in view of the significant cooling of the quality of life and evolution often severe that characterizes the clinical course of these patients. Revascularization Surgery is the treatment of choice, but about half of patients with severe PAD IIb is not eligible for surgery or endovascular treatment. The usefulness of use of vasodilators or hemorheological is controversial, and medical treatment of these patients is therefore heterogeneous understanding the various pharmacologic options (for the correction of risk factors, prevention of cardiovascular events, improvement of claudication), and rehabilitative programs. Iloprost, a synthetic analogue of prostacyclin, is effective in the treatment of patients with chronic critical ischemia, and its pharmacological profile (effective vasodilator, anti-platelet, and leukocyte activation) is particularly suitable to modulate multiple components pathogenesis of peripheral arterial disease. Specifically, in the treatment of patients with PAD IIb severe, the current state is available only a retrospective study that compared the use of iloprost with that of vasodilators. Aim of the study FADOI-2bPILOT is to evaluate prospectively and for an observation period of 13 months, if you can get a benefit on the pain-free walking distance and on clinical outcome from "anticipated" and additional use of iloprost, in patients with severe IIb stage PAD treated according to current "best medical practice".