Objective: This study tested the reliability of the ORI laxometer, a newly developed non-invasive device for testing inferior translation of the humeral head in humans. Design: The instrument was designed to measure displacement between the top of the acromion and the head of the humerus when loaded in a similar fashion to the sulcus sign. Participants and interventions: Sixteen healthy subjects (32 shoulders) were measured for inferior glenohumeral joint laxity. One observer used the laxometer in 16 subjects on three separate occasions for the intraobserver trial. Three observers measured the inferior shoulder laxity of six subjects on one occasion in the interobserver trial. Asymptomatic and unstable shoulders were also compared in 12 subjects with shoulder instability. Main outcome measurements: Translation in the glenohumeral joint Results: The range of inferior translation of glenohumeral joint in these subjects was between 0.01 mm and 6.5 mm with a mean of 1.5 mm. The intraclass correlation coefficient (ICC) for inter-observer reliability was 0.74. For intra-observer reliability the ICC was 0.76. These results are considered to be good to excellent. There was no advantage gained by using data from all five cycles of testing compared with three cycles. In patients with shoulder instability, laxometer measurements were significantly greater in their unstable shoulders than in their normal shoulders. Conclusions: The laxometer is easy to use, painless and gives objective measures for inferior glenohumeral laxity, with good intra- and inter-observer reliabilities. The ORI laxometer may be useful for assessing and monitoring global glenohumeral joint laxity which usually involves inferior laxity.