Assessing laxity of the shoulder joint in patients who are under anesthesia is a standard procedure before arthroscopy. The aim of this study was to evaluate a novel instrument for quick and reliable intraoperative measurement of glenohumeral translation. Previous testing of various designs has resulted in a device secured by 1 pin in the acromion and 1 pin in the proximal humerus. These pins are interconnected by a sliding ruler that gives translation values in millimeter increments as the laxity tests are performed. Comparison between manual arbitrary approximation of laxity and instrumented translation measurements showed that manual testing is reasonably good for assessment of anterior and posterior translation, without, however, providing values of translation in millimeter increments. The low correlation between manual assessment and instrumented inferior translation measurements indicates that inferior translation is more difficult to approximate manually. The shoulder translation tester was used in 102 patients. The mean values for clinically stable shoulders (n = 58) were 5 mm for anterior translation, 5 mm for posterior translation, and 4 mm for inferior translation. The corresponding values in unstable shoulders were significantly higher than in the stable shoulders, especially in patients with multidirectional instability. We conclude that the shoulder translation tester is easy and quick to use. It provides quantitative values of translation and will thus contribute information for correct diagnosis, therapy, and documentation.