Zones of hypovascularity are thought to exist in several tendons of the shoulder, contributing to localized tendon weakness and subsequent rupture in clinical practice. Although these zones have been demonstrated in many frequently ruptured tendons, the existence of a similar area in the often ruptured long head of biceps (LHB) tendon is largely unknown. Twenty cadaveric upper limb specimens were dissected after injection with either a radio-opaque lead oxide/milk mixture or India ink, followed by histological sectioning of the tendons. The LHB tendon was consistently supplied via its osteotendinous and musculotendinous junctions by branches of the thoracoacromial and brachial arteries respectively. In two specimens, additional branches from the anterior circumflex humeral artery travelling in a mesotenon vascularized the midsection of tendon. These source arteries divided the LHB tendon into either two or three vascular territories, depending upon the presence of the mesotenon-derived vascular supply. A zone of hypovascularity was consistently found in the region of the LHB tendon most frequently prone to rupture. This zone covered an area 1.2–3 cm from the tendon origin, extending from midway through the glenohumeral joint to the proximal inter-tubercular groove. This hypovascular region occurred on the border of two adjacent vascular territories, where reduced caliber choke vessels provide limited arterial supply. While it is probable that the limited arterial supply contributes to the susceptibility of this area to rupture, similar to other tendons the true pathogenesis is likely to be a combination of both vascular and mechanical factors. Clin. Anat. 23:683–692, 2010. © 2010 Wiley-Liss, Inc.