To assess the effect of acute angle closure glaucoma (AACG) and related surgical intervention on the corneal endothelium, specular microscopy was performed following surgery in a series of 69 patients: 27 for AACG, 9 for incipient angle closure, 17 for chronic angle closure glaucoma (CACG), and 16 for chronic open angle glaucoma (COAG). Peripheral iridectomy for incipient angle closure glaucoma caused no significant effect on the corneal endothelium, but, following peripheral iridectomy or drainage operation for AACG, significant lowering of the endothelial cell count was present in the affected eye (p less than 0.05) with 1,000 cells/mm2 in 7 cases. This was related to the presence of segmental iris atrophy (p less than 0.01). Peripheral iridectomy for CACG or incipient angle closure glaucoma was not accompanied by a significant effect, but drainage operation for CACG or COAG was associated with a significant fall in count (p less than 0.01). Thus, both AACG and drainage operation significantly affect the corneal endothelium, and this should be assessed before undertaking further surgery.