Background. Shoulder pain limits range of motion (ROM) and reduces performing activities of daily living (ADL). Objective assessment of shoulder function could be of interest for diagnosing shoulder pathology or functional assessment of the shoulder after therapy. The feasibility of 2 wearable inertial sensors for functional assessment to differentiate between healthy subjects and patients with unilateral shoulder pathology is investigated using parameters as asymmetry. Methods. 75 subjects were recruited into this study and were measured for at least 8 h a day with the human activity monitor (HAM) sensor. In addition, patients completed the Disability of the Arm, Should and Hand (DASH) score and the Simple Shoulder Test (SST) score. From 39 patients with a variety of shoulder pathologies 24 (Age: 53.3 ± 10.5;% male: 62.5%) complete datasets were successfully collected. From the 36 age-matched healthy controls 28 (Age: 54.9 ± 5.8;% male = 57.1%) full datasets could be retrieved. Activity parameters were obtained using a self-developed algorithm (Matlab). Outcome parameters were gyroscope and accelerometry-based relative and absolute asymmetry scores (affected/unaffected; dominant/non-dominant) of movement intensity. Results & Discussion. The absolute and relative asymmetry scores of the accelerometry-based intensity results for a threshold of > 0.1 g (AUC 0.821 and AUC 0.827) proved to be slightly more distinctive to the gyroscope-based intensity results for a threshold of > 10 deg/s (AUC 0.807 and 0.795) to distinguish between the healthy group and the shoulder group. Asymmetry (< 1%) was nearly absent in healthy controls (5/56 subjects) using the accelerometry-based intensity (> 0.1g) results but common in patients (29/48 subjects). A moderate, significant correlation was found between the asymmetry scores and the DASH score, thus complementary use is advised. The asymmetry scores had no correlation to the SST score. Conclusion. Ambulant assessment of shoulder activity using human activity monitors, containing a gyroscope and accelerometer, during ADL is feasible. The accelerometry-based and gyroscope-based absolute and relative asymmetry scores are promising parameters to diagnose or assess function of the shoulder. A moderate correlation was found between the DASH score and the activity monitor parameters, suggesting both could be used complementary to assess function