Purpose: To report supraciliochoroidal effusion after trabeculectomy with the use of ultrasound biomicroscopy. Methods: ln a prospective study 30 eyes of 19 patients with primary open- angle glaucoma that underwent trabeculectomy were evaluated preoperatively and postoperatively by ultrasound biomicroscopy. Results: 3 eyes showed a hypoechogenic suprachoridal space that remained stable for 6 months postoperatively. These 3 eyes had intraocular pressures of 11mnHg or less on no antiglaucoma medications and without signs of choroidal detachment. Collusion: Ultrasound biomicroscopy proved to be a useful method of detecting, after trabeculectomy, supraciliochorodal fiuid without clinically detectable chorodal detachment. This fluid may signify an iatrogenic cyclodialysis durng surgery or less likely, subclincal ciliochoridal detachment.