the european medicinal leech has been used for medicinal purposes for millennia, and continues to be used today in modern hospital settings. its utility is granted by the extremely potent anticoagulation factors that the leech secretes into the incision wound during feeding and, although a handful of studies have targeted certain anticoagulants, the full range of anticoagulation factors expressed by this species remains unknown. Here, we present the first draft genome of the European medicinal leech, Hirudo medicinalis, and estimate that we have sequenced between 79-94% of the full genome. Leveraging these data, we searched for anticoagulation factors across the genome of H. medicinalis. following orthology determination through a series of BLASt searches, as well as phylogenetic analyses, we estimate that fully 15 different known anticoagulation factors are utilized by the species, and that 17 other proteins that have been linked to antihemostasis are also present in the genome. We underscore the utility of the draft genome for comparative studies of leeches and discuss our results in an evolutionary context. Notwithstanding the significance of the European medicinal leech Hirudo medicinalis Linnaeus, 1758 as a medical tool from antiquity through modern science-based medicine, it is remarkable that this species' repertoire of anticoagulants and other bioactive salivary proteins has escaped published in-depth investigation (but see 1). In order to maintain blood flow in the tissues surrounding the incision wounds during their extended periods of feeding and, importantly, keeping the blood from clotting inside of the crop during the periods of digestion, bloodfeeding leeches secrete a variety of bioactive compounds from their salivary glands. Over 20 different compounds relating to antihemsotasis have been isolated from leech saliva including, for example, direct thrombin inhibitors, factor Xa inhibitors, trypsin inhibitors, endoglucuronidases and antiplatelet proteins 2,3. Despite its historical significance in medicine, the detailed composition of the anticoagulant profile of Hirudo medicinalis Linnaeus, 1758 has escaped scrutiny insofar as modern studies have been concerned primarily with the commercially available species Hirudo verbana (Carena, 1820) 4-7 ; but see also 1,8. Whereas H. medicinalis was long thought to be the centerpiece for the clinical application of leeches in hospital settings, recent investigations have shown that Hirudo verbana is far more commonly employed for this purpose 4 yet sold under the name H. medicinalis; this confusion also prompted the designation of a neotype specimen for H. medicinalis in order to ameliorate future taxonomic confusion 9. The utility of leeches in modern medicine focuses on post-surgical procedures, chiefly following digit replantation or skin grafting surgery 10,11 wherein the build-up of blood in the extremities and resulting congestion of the veins is relieved by their application. By contrast, medieval medicinal practices,