The purpose of this study was to investigate shoulder activity level in preoperative assessment of shoulder function and health-related quality of life (QoL) for patients with rotator cuff tears. One hundred and six patients with rotator cuff tears were prospectively evaluated using the following outcome instruments: the Shoulder Activity scale, the Constant scale, the Simple Shoulder Test, and the Short Form-36v2 (SF-36v2). Clinical and structural data, including patients’ demographics, comorbidities, duration of symptoms, shoulder contracture, and tear size, were collected and analyzed. We determined that the shoulder activity level was associated with gender, medical comorbidities, and age. Females had lower activity level, worse scores for health-related QoL, and longer duration of symptoms than males. Patients who had severe comorbidities had lower shoulder activity scores and worse SF-36v2 scores compared to patients who did not have such comorbidities. The patient age correlated with the shoulder activity level, but did not have significant correlation with the duration of symptoms and shoulder function. The shoulder activity level was related to patient gender, general health status and age; therefore, further investigation is warranted to determine if the activity level can be used as a prognostic variable relating to outcome in the treatment of rotator cuff tears.