BACKGROUND Electromagnetic tracking systems have enabled some investigators and clinicians to measure tri-planar scapular motion; yet, they are not practical and affordable options for all clinicians. Currently, the ability to affordably quantify scapular motion is limited to monitoring only the motion of scapular upward rotation, with use of a digital inclinometer. HYPOTHESIS/PURPOSE The objective of this study was to determine the criterion-related validity of a modified digital inclinometer when used to measure the motion of scapular anterior-posterior (AP) tilt. MATERIALS & METHODS Thirteen volunteers, free from any history of shoulder injury, reported for a single testing session. Each subject underwent a brief shoulder and posture examination in order to confirm the absence of pathology. Subjects actively performed clinically relevant amounts of humeral elevation in the scapular plane while in a seated position. An electromagnetic tracking system (Ascension Technology, Burlington, VT) and a modified inclinometer (Pro 360, Baseline®, Fabrication Enterprises, White Plains, NY) were used to acquire scapular AP tilt over the same shoulder motions. Criterion-related validity was determined using Pearson Product Moment correlations. RESULTS Correlation analyses revealed significant moderate to good associations (r = 0.63 to 0.86, p < 0.01) between scapular AP tilt measures obtained with a digital inclinometer and an electromagnetic tracking system. CONCLUSIONS A modified digital inclinometer is a moderately valid device to use for the quantification of scapular AP tilt. Further study is warranted to establish reliability and to validate use of the device in patients with shoulder injury or pathology. The modified inclinometer expands the clinician's ability to quantify scapular kinematic motion during the clinical evaluation and rehabilitation process. LEVEL OF EVIDENCE Level 3.