Objective: First, to compare the reliability of measuring shoulder internal rotation (IR) range of motion (ROM) using three different techniques: sidelying, or sleeper stretch position (SSP), scapular stabilization (SS), and visual inspection (VI). Second, to establish and compare shoulder IR ROM characteristics using SSP, SS, and VI in the dominant and non-dominant arms of overhead and non-overhead athletes. Background: Many studies have reported that decreased shoulder IR ROM is associated with shoulder pathology. However, no single method for measuring shoulder IR ROM has demonstrated consistently high levels of reliability. The sleeper-stretch is often used to increase shoulder IR ROM yet there are no known studies presenting shoulder IR ROM characteristics in athletes as measured with the SSP. Method: Twenty male subjects asymptomatic of upper extremity injury were recruited for the reliability phase. Shoulder IR passive ROM was measured on both arms by two examiners using three techniques: SSP, SS, and VI. In the second phase, 25 overhead and 25 non-overhead collegiate athletes were recruited. Shoulder IR passive ROM values were obtained on the dominant and non-dominant arms of each athlete using the three techniques. Results: Intrarater reliability was good for SSP, good for SS and fair to good for VI. Interrater reliability for SSP was excellent, good for SS and good for VI. The dominant arm of non-overhead athletes had significantly lower IR ROM tha overhead athletes using SSP. In both overhead and non-overhead athletes, IR ROM was signficantly less using SSP and SS compared to VI in the dominant and non-dominant arms. Conclusion: When measuring shoulder IR passive ROM, SSP had better interrater reliability compared to SS or VI. Significantly lower IR was found in the dominant arm of non-overhead athletes versus overhead athletes. Internal rotation in the dominant arm of overhead athletes was significantly lower than their non-dominant side.