The purpose of this study was to determine if glenohumeral internal rotation deficits (GIRD) exist in an asymptomatic population of professional pitchers, and to assess whether these changes are primarily a bony or soft tissue adaptation. Twenty three, active, asymptomatic professional (Major League Baseball) pitchers volunteered for the study. Clinical measures of glenohumeral ranges of motion, laxity, GIRD, as well as radiographic measures of humeral retroversion were taken by two independent orthopaedic surgeons. Data comparing side to side differences in range of motion, laxity, and humeral retroversion were analyzed for statistical significance using a paired t-test for continuous data and a Chi-squared test for ordinal data, with a significance set at 0.05. Evaluations of statistical correlations between different measurement parameters were accomplished using a Pearson product moment correlation. We hypothesized GIRD will be positively correlated with humeral retroversion (HR) in the pitching arm. All clinical and radiographic measures were made in the field, at spring training, by physicians of both private and institutional based sports medicine practices. For the entire group, significant differences were exhibited for HR, external rotation at 90° and internal rotation at 90°, for dominant vs. non-dominant arms. GIRD of greater than 25° was noted in 10/23 of pitchers. In this group, HR was significantly increased and correlated to GIRD. No such increase or correlation was noted for the non-GIRD group. GIRD is a common finding in asymptomatic professional pitchers, and is related to humeral retroversion. Thus internal rotation deficits should not be used as the sole screening tool to diagnose the disabled throwing shoulder.