The records of 27 patients who developed retinal arterial obstruction (RAO) prior to the age of 30 years were studied to ascertain associated systemic and ocular findings as possible etiologic factors. A history of migraine was found in approximately one third of the patients, and coagulation abnormalities wer also common. Trauma, sickle cell hemoglobinopathies, cardiac disorders, use of oral contraceptives, pregnancy, systemic lupus erythematosus and intravenous drug abuse were less frequently encountered. Ocular abnormalities included increased intraocular pressure, subtle buried drusen of the optic nerve head and a congenital prepapillary arterial loop. In contrast to older patients with RAO, there was no clinical evidence of atheromatous disease. In most patients, one or more systemic or ocular etiologic factors could be discerned. Whereas etiologic relationships may be multifactorial and generally differ from those commonly found in older patients with RAO, the visual prognosis in younger and older patients appears to be similar.