Nitinol is a near-equiatomic alloy of nickel and titanium which has a wide range of applications due to its outstanding functional properties, such as shape memory and superelastic behavior. Superelastic nitinol wires, often used for the fabrication of stents, exhibit recoverable strains that are significantly greater than traditional alloys. This property arises from the transformations between the two phases, austenite and martensite, that it adopts near room temperature. In most of its applications, nitinol is cycled between these two phases, which results in functional and/or structural fatigue that ultimately leads to failure. It has been shown that the main fatigue crack initiation sites, other than surfaces, are microstructural inhomogeneities such as voids and non-metallic inclusions. In this work, nitinol wires with three different sizes are subjected to microstructural analysis and low-cycle fatigue tests to understand the effect of wire size on phase transformations and fatigue crack nucleation around non-metallic inclusions.