We studied four patients with idiopathic dilated episcleral vessels. Three of these patients had asymmetric or unilateral open-angle glaucoma in the eye with the greater degree of episcleral vascular anomaly. The fourth patient showed dilated episcleral vessels, but the intraocular pressure (IOP) was not increased. In the three patients with increased IOP, the facility of outflow was decreased. The episcleral venous pressure was not measured, but in one eye Schlemm's canal was engorged with blood despite an IOP of 35 mm Hg. We explored the possibility of a congenital vascular anomaly in the four cases.