PURPOSE. To determine the prevalence of appositional angle closure (AAC) after laser peripheral iridotomy (LPI) in the eyes of Chinese patients with primary angle closure (PAC) and primary angle closure glaucoma (PACG) and to evaluate its pathogenesis by investigating anatomic characteristics. METHODS. This was a cross-sectional observational study. PAC and PACG subjects were consecutively enrolled after LPI. Ultrasound biomicroscopy (UBM) images, obtained in darkness, of each quadrant without peripheral anterior synechia (PAS) under gonioscopy were qualitatively assessed. Darkroom provocative test (DRPT) was also performed. RESULTS. A total of 134 eyes of 134 patients were enrolled. AAC was observed in >= 1 quadrant of UBM image in 85 subjects (63.4%). There were 116 randomly selected quadrants without PAS for 134 patients (86.6%). AAC existed in 38 quadrants (32.8%). Among these, plateau iris accounted for 44.7%, anteriorly inserted iris for 13.2%, thick iris for 13.2%, and anteriorly inserted iris combined with thick iris for 18.4% of the total. One hundred fifteen patients underwent DRPT and its positive rate of eyes with AAC >= 2 quadrants (37.5% [12 of 32 patients]) was significantly higher than those <= 1 quadrant (16.9% [14 of 83 patients]; P = 0.018). However, no significant differences were found between eyes with nonsynechia plateau iris >= 2 quadrants (36.4% [4 of 11 patients]) and those <= 1 quadrant (21.2% [22 of 104 patients]; P = 0.266). CONCLUSIONS. Approximately two-thirds of PAC and PACG eyes of Chinese patients after LPI had AAC. Plateau iris accounted for less than 50% of AAC. Other factors such as a thick peripheral iris and an anteriorly inserted iris also contributed to AAC. DRPT results suggested AAC might have more functional meaning than plateau iris.