To characterize short-term changes induced by pars plana vitrectomy on anterior segment depth and lens thickness by means of high-frequency ultrasound biomicroscopy. We undertook a prospective case series study on consecutive patients referred for pars plana vitrectomy as the sole procedure in our institution between 2005 and 2007. Twenty-eight eyes of 28 patients undergoing pars plana vitrectomy were studied by ultrasound biomicroscopy. Neither silicone oil nor scleral buckle was used for any of the procedures. Anterior chamber depth and lens thickness were compared before and immediately after surgery, and their results were compared to the postoperative intraocular pressure measurements. There was a significant decrease in anterior chamber depth in the study eyes of patients who had undergone gas tamponade (p<0.0001) but not in those who had not undergone gas tamponade. No differences were found between the preoperative and the postoperative lens thickness measurements in any of the patients, nor was there any correlation between anterior chamber depth and increased intraocular pressure. Uncomplicated pars plana vitrectomy with gas tamponade can induce short-term changes in anterior chamber depth as measured by morphometry. Surgeons may need to reconsider using gas tamponade at the end of surgery in surgical candidates with shallow anterior chambers.