Purpose To determine the distribution and the anatomical characteristics of plateau iris (PI) in primary angle closure glaucoma (PACG) using ultrasound biomicroscopy (UBM). Methods Fifty UBM images of PACG cases were studied over one year by retrospective analysis. The data from UBM images including angle opening distance at 500 and 750 μm (AOD500 and AOD750), trabecular-iris angle (TIA), angle recess area at 750 μm (ARA750), maximum ciliary body thickness (CBTmax), anterior placement of ciliary processes (APCP), central anterior chamber depth (CACD), axial lens thickness (ALT), and ciliary sulcus status were analyzed and compared between the PI and non-PI cases. Results Eighteen cases had PI (36%). The mean AOD500, AOD750, and TIA were significantly smaller in PI than in non-PI eyes ( P = 0.01; P = 0.046; and P = 0.026). Values of the ARA750 and CBTmax were not significantly different between the two groups ( P = 0.208 and P = 0.368). CACD was deeper in the PI group ( P = 0.011). ALT was higher in the non-PI group ( P = 0.001). The mean APCP of the PI group was more than those of the non-PI group ( P < 0.001). The number of cases with obliterated ciliary sulcus in more than two quadrants was significantly more in the PI group ( P < 0.001). Conclusion Around one-third of PACG eyes were found to have PI on UBM imaging. The number of obliterated ciliary sulcus and APCP were important UBM parameters that help in PI diagnosis.