AbstractObjectivesTo investigate the role of the inferior glenohumeral capsule (IGHC) ratio in diagnosing frozen shoulder (FS) by analysing two patient groups with shoulder dysfunction, one with and the other without clinical signs of FS.MethodsThis study was performed in volunteers with unilateral shoulder problems. Passive ranges of motion were measured, and pre‐defined clinical criteria were used to allocate participants into FS and no‐FS groups. IGHC ratios were calculated at shoulder abduction angles of 60° and 90°. The Independent‐Samples‐Mann–Whitney U test was used to compare the distributions of the IGHC ratios of the two groups.ResultsOf 151 participants (53 years ± 7, 78 men), 13 fulfilled the FS criteria. All participants were measured at 60° abduction. Eight of the FS and 127 of the no‐FS groups were able to be measured at 90°. A significant group difference was found in the IGHC ratios at 90° abduction (p = .008, FS group = 1.8, no‐FS group = 1.1) but not at 60° (p = .31). At 90° abduction, an IGHC ratio ≥1.8 was 92% specific to the FS cohort. In those without clinical signs of FS, no difference was found in IGHC thicknesses between the symptomatic and asymptomatic sides.ConclusionThe ultrasound IGHC thickness ratio obtained at 90° shoulder abduction has potential for confirming the clinical suspicion of FS in those who can abduct their shoulders to 90°. The contralateral shoulder used for comparison does not have to be symptom free as long as it does not exhibit clinical signs of FS.