To evaluate the prevalence of plateau iris diagnosed by ultrasound biomicroscopy after laser peripheral iridotomy in Whites as compared to Asians in a U.S. clinic setting.This was a prospective, observational study of narrow angle patients (n=55) who underwent laser peripheral iridotomy. Ultrasound biomicroscopy was performed in 4 quadrants of only one eye of each patient 4~6 weeks before and after surgery. The images were randomized and interpreted qualitatively by a single observer. Plateau iris was diagnosed in eyes with persistent appositional angles after laser peripheral iridotomy when at least 2 quadrants fulfilled the following criteria: 1. The ciliary process was directed anteriorly. 2. The ciliary sulcus was absent. 3. The central iris plane was flat.Twenty eight subjects (50.1%) were Whites, and 27 subjects (49.0%) were Asians. Plateau iris was assessed in 18 subjects (32.7%): 9 of 28 Whites (32.1%) and 9 of 27 Asians (33.3%). The proportion of plateau iris did not differ between Whites and Asians (P>0.99)The prevalence of plateau iris did not differ between Whites and Asians. Both groups had a substantial proportion of narrow angle patients with this clinical entity.