In 1998, a 76-year-old woman with primary open-angle glaucoma had a latanoprost-induced iris cyst in her right eye. The cyst gradually resolved after substitution of latanoprost with topical timolol.1 During the following 2 years, the intraocular pressure increased to levels greater than 20 mm Hg. After obtaining informed consent, the right eye was rechallenged with latanoprost, 0.005%, at bedtime. At examination 7 months later, the iris cyst had recurred and led to anterior displacement of the iris in the inferotemporal quadrant. Due to lasting elevated intraocular pressure and the lack of any complications from the cyst, the patient continued to receive latanoprost therapy for approximately 2.5 years (until 2003). Then, an attempt to reduce the intraocular pressure was made by replacing latanoprost with bimatoprost, 0.03%, once every evening, which shortly thereafter resulted in a further increase in cyst size. The cyst bulged the iris forward between the 6- and 10-o’clock positions (Figure 1) and was visible as a slightly transilluminating, elongated, dark brown mass just posterior to the pupillary margin. The color and pigmentation of the iris stroma were normal, and there were no signs of intraocular inflammation. Ultrasound biomicroscopy demonstrated a solitary, thin-walled cyst with clear intracavitary fluid posterior to the iris. The cyst, measuring 1.5 × 4 mm, extended from the iridociliary junction to the pupillary border (Figure 2A). Owing to planned cataract surgery of the right eye, bimatoprost treatment was discontinued; periodic slitlamp examinations showed that the cyst gradually diminished and finally disappeared within the following 6 weeks. Despite normal configuration of the anterior chamber and iris surface, repeated ultrasound biomicroscopy revealed a small cystic structure persisting close to the junction between the iris and ciliary body (Figure 2B).