An anteroinferior portal can be safely used in arthroscopic shoulder surgery but requires an in-depth knowledge of axillary nerve anatomy. The purpose of this report is to present the qualitative and spatial anatomy of the axillary nerve and to describe patterns of arborization that may affect safe anteroinferior arthroscopic portal placement. Measurements were taken in 42 embalmed cadaveric shoulders (20 male, 22 female). The distance from the acromioclavicular (AC) joint to the axillary nerve averaged 7.90 cm (range, 7.2 to 9.1 cm) in males and 6.37 cm (range, 5.2 to 8.1 cm) in females. We describe the axillary nerve index (distance of nerve from the AC joint/length of deltoid from AC joint) which can be used to predict the location of the axillary nerve along the anterior clavicular line (ACL). The axillary nerve index averaged 0.48 (range, 0.42 to 0.57) in males and 0.41 (range, 0.31 to 0.57) in females. Four types of morphology were noted in the axillary nerve: (1) main trunk with superior and inferior branches, (2) main trunk with superior branches, (3) main trunk with inferior branches, and (4) main trunk only. Our work supports the traditional operable safe zone for the axillary nerve.