Purpose To compare the accuracy in measurement of the anterior chamber (AC) angle by anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) in European patients with suspected primary angle closure (PACS), primary angle closure (PAC), or primary angleclosure glaucoma (PACG). Design Cross-sectional study. Methods In all, 55 eyes of 33 consecutive patients presenting with PACS, PAC, or PACG were examined with AS-OCT, followed by UBM. The trabecular-iris angle (TIA) was measured in all four quadrants. The angle-opening distance (AOD) was measured at 500 lm from the scleral spur. The BlandAltman method was used for assessing agreement between the two methods. Results The mean (±SD) superior TIA was 19.3 ± 15.81 in AS-OCT and 15.7 ± 15.01 in UBM (P ¼ 0.50) and inferior TIA was 17.9 ± 12.91 (AS-OCT) and 16.7 ± 14.11 (UBM) (P ¼ 0.71). The superior AOD 500 was 0.17 ± 0.16 mm in UBM and 0.21 ± 0.16 mm in AS-OCT (P ¼ 0.06). BlandAltman analysis showed a mean SD of±9.41 for superior and inferior TIA and a mean SD of ±0.10 mm for superior and inferior AOD 500 .Conclusions This comparative study shows that AS-OCT measurements are significantly correlated with UBM measurements but show poor agreement with each other. We do not believe that AS-OCT can replace UBM for the quantitative assessment of the AC angle.