Background: The most frequent condition affecting the shoulder is likely subacromial impingement syndrome (SIS). Although there is evidence linking upper body posture and shoulder function, there is no evidence linking posture to SIS. Objective: To determine the relation between aberrant upper body posture and shoulder ROM. Also, to determine the relation between aberrant upper body posture and shoulder disability levels in cases of SIS. Patients and Methods: The study included 37 subjects with SIS (group B), their mean age was 28 years, (male & female) and 37 age and gender-matched controls (group A). Upper body posture was analysed using bubble inclinometer for thoracic kyphosis (TK) measurement, lateral scapular slide test (LSST) for detecting scapular dyskinesia (SD), tape for pectoralis minor length measurement. Results: There was statistically significant reduction in mean values of kyphosis in favor to control group (P=0.027). But there was statistically significant increase in mean values of pectoralis minor length in favor of control group (P=0.033). Also, no statistically significant differences in mean values of LSST at the three different positions were found between both groups (P > 0.05). Within the SIS group there was no statistical significant correlation between aberrant upper body posture (thoracic kyphosis, scapular dyskinesia and pectoralis minor length) and passive shoulder flexion ROM, passive shoulder abduction ROM, shoulder pain and disability levels. Conclusion: Patients with SIS had a more exaggerated TK and less pectoralis minor length and no difference in scapular position compared to age- and sex-matched normal controls.