Background: Angle-closure glaucoma in children at the cicatricial stage of retinopathy of prematurity (ROP) has been thought to be caused by the anterior displacement of the lensiris diaphragmresulting from contraction of a retrolental fibrous membrane. Other possible mechanisms include pupillary block and ciliary block. Cases: Three patients (three eyes) at the cicatricial stage of ROP with angle-closure glaucoma were examined by high-resolution ultrasonography before and after peripheral iridectomy. Observations: High-resolution ultrasonography preoperatively showed that the angle was closed. A retrolental fibrous membrane was attached behind the lens. After the iridectomy, ultrasonography showed an open angle, and the intraocular pressure was normal. Conclusions: The angle closure in our three patients was caused mainly by a pupillary block and could be treated by peripheral iridectomy. Background: Angle-closure glaucoma in children at the cicatricial stage of retinopathy of prematurity (ROP) has been thought to be caused by the anterior displacement of the lensiris diaphragmresulting from contraction of a retrolental fibrous membrane. Other possible mechanisms include pupillary block and ciliary block Cases: Three patients (three eyes) at the cicatricial stage of ROP with angle-closure glaucoma were examined by high-resolution ultrasonography before and after peripheral iridectomy. Observations: High-resolution ultrasonography preoperatively showed that the angle was closed. A retrolental fibrous membrane was attached behind the lens. After the iridectomy, ultrasonography showed an open angle, and the intraocular pressure was normal. Conclusions: The angle closure in our three patients was caused mainly by a pupillary block and could be treated by peripheral iridectomy.