['Baseball pitchers often have increased anterior glenohumeral (GH) laxity and posterior shoulder tightness due to large forces produced during the throwing motion. As such, many clinicians have hypothesized that a relationship exists between these common characteristics.', 'A negative relationship will exist between anterior GH laxity and the summation of GH adduction range of motion (ROM) and GH internal rotation ROM asymmetry.', 'Cross-sectional study; Level of evidence, 3.', 'Anterior GH laxity, GH rotation ROM, and GH horizontal adduction ROM were measured in 58 asymptomatic professional baseball pitchers. Differences in GH internal rotation at 90° of abduction were calculated between both shoulders. A multiple regression analysis was used to determine the strength of the relationships between anterior GH laxity (dependent variable) and GH adduction ROM and GH internal rotation ROM asymmetry (independent variables) (P < .05).', 'A large portion of anterior GH laxity was predicted by the summation of GH adduction ROM and GH internal rotation ROM asymmetry (r (2) = .45, P = .001). Furthermore, increased anterior GH laxity had a significant relationship with both decreased GH horizontal adduction ROM (r = .53, P = .001) and differences in GH internal rotation ROM (r = .43, P = .001).'] Is anterior glenohumeral laxity associated with posterior shoulder tightness among professional baseball pitchers?