Objective: To evaluate the role of annular ciliary body detachment in the development of postoperative angle-closure glaucoma. Design: Case series. Setting: Tertiary care glaucoma referral center. Methods: High-resolution, anterior segment ultrasound biomicroscopy, ophthalmoscopy, and B-scan ultrasonography were performed on 6 eyes of 6 patients with a clinical diagnosis of postoperative malignant glaucoma. Results: Each eye had an elevated intraocular pressure, a shallow anterior chamber, I or more patent iridectomies, and no ophthalmoscopic or B-scan ultrasound evidence of serous or hemorrhagic ciliochoroidal detachment. Ultrasound biomicroscopy revealed annular ciliary body detachment in each eye. In 4 eyes, observation with topical medical treatment was associated with deepening of the anterior chamber, reduced intraocular pressure, and resolution of the detachment. Drainage of the supraciliary fluid was performed in 2 eyes. Conclusion: Occult, annular, serous detachment of the ciliary body may cause postoperative angle-closure glaucoma. This entity is clinically indistinguishable from malignant glaucoma. Ultrasound biomicroscopy facilitates the diagnosis.