Objectives: To describe and illustrate the ultrasound biomicroscopic findings in patients with one or more cystic lesions of the iris, ciliary body, or both.Methods: Retrospective study of 263 ultrasound biomicroscopic studies performed at one institution during a 20-month period, May 1994 through December 1995. All studies were performed using the Humphrey ultrasound biomicroscope model 840.Results: Thirty-nine of the 263 evaluated patients had one or more cystic lesions. Four different types of cysts were detected. Twenty-seven patients had one or more primary neuroepithelial cysts of the iris or ciliary body. These cysts were frequently multifocal and bilateral. All contained clear fluid and had a thin but highly reflective wall. Three patients had a stratified squamous epithelial implantation cyst. These cysts were all unifocal and unilateral. The intracavitary fluid contained multiple suspended particles (presumably desquamated epithelial cells), and the walls were relatively thick. Six patients had a neuroepithelial cyst associated with a solid tumor. Each of these cysts resembled the primary neuroepithelial cysts. Three patients had focal intratumoral cavitation. The cavity in each case contained clear fluid. The surrounding tumor tissue in each case appeared homogeneous.Conclusions: Ultrasound biomicroscopy appears to be a valuable clinical tool for evaluating and differentiating cystic lesions of the iris and ciliary body.