Objective: To compare three dimensional movement patterns of the affected and non-affected shoulder in patients with a frozen shoulder before and after physical therapy. Methods: Patients with a unilateral frozen shoulder were assessed before and after three months of treatment. Three dimensional movement analysis was performed with the "Flock of Birds" electromagnetic tracking device while the patient raised their arms in three directions. Slopes of the regression lines of glenohumeral joint rotation versus scapular rotation, reflecting the scapulohumeral rhythm, were calculated. All assessments were made for both the affected and the unaffected side. Additional assessments included conventional range of motion (ROM) measurements and visual analogue scales (VAS) (0-100 mm) for shoulder pain at rest, during movement, and at night. Results: Ten patients with a unilateral frozen shoulder were included. The slopes of the curves of the forward flexion, scapular abduction, and abduction in the frontal plane of the affected and the unaffected side were significantly different in all three movement directions. Mean differences were 0.267, 0.215, and 0.464 (all p values <0.005), respectively. Mean changes of the slopes of the affected side after treatment were 0.063 (p=0.202), 0.048 (p=0.169), and 0.264 (p=0.008) in forward flexion, scapular abduction, and abduction in the frontal plane, respectively. All patients showed significant improvement in active ROM (all p<0.005), and the VAS for pain during movement and pain at night (p<0.05). Conclusions: With a three dimensional electromagnetic tracking system the abnormal movement pattern of a frozen shoulder, characterised by the relatively early laterorotation of the scapula in relation to glenohumeral rotation during shoulder elevation, can be described and quantified. Moreover, the system is sufficiently sensitive to detect clinical improvements. Its value in other shoulder disorders remains to be established.