ABSTRACT.Purpose: The aim of this study was to evaluate changes in the anterior chamber depth (ACD) in primary open-angle glaucoma (POAG) patients during latanoprost therapy. Methods: We carried out a prospective study in which we enrolled 66 newly diagnosed POAG patients treated with latanoprost 0.005% (group 1) and 50 ocular hypertensive and ⁄ or glaucoma suspect cases who were given no therapy (group 2 [control]). Measurements of the ACD were performed by A-scan ultrasonography before and after cycloplegia at baseline and at 3 months of latanoprost therapy. Differences in ACD and their correlations with the ocular hypotensive effect of the agent as well as the clinical significance of changes in ACD were analysed using Student's t-test and Pearson's correlation coefficient. Statistical significance was set at p < 0.05. Results: Mean baseline ACD was 3.13 ± 0.35 mm (range 2.45-3.84 mm) in group 1 and 3.14 ± 0.36 mm (range 2.54-3.80 mm) in group 2 (p = 0.89). At 1 hour after instillation of cyclopentolate 1%, mean ACD in groups 1 and 2 was 3.18 ± 0.38 mm (range 2.45-3.92 mm) and 3.19 ± 0.37 mm (range 2.56-3.91 mm), respectively (p = 0.91). After 3 months of treatment, mean ACD in group 1 both without (3.05 ± 0.36 mm, range 2.14-3.76 mm) and with (3.09 ± 0.4 mm, range 2.20-3.96 mm) cycloplegia was significantly reduced compared with baseline values (p < 0.001 for both). However, there was no significant difference between mean ACD at baseline and that at month 3 in group 2. No correlation was demonstrated between the changes in ACD and the ocular hypotensive effect of latanoprost (p = 0.96, r = ) 0.006). There were no changes in refractive status or visual acuity. Conclusions: The overall results seem to suggest that latanoprost decreases mean ACD in patients with POAG. The clinical significance of this effect is uncertain.