OBJECTIVE The purpose of study A was to assess the effectiveness of vitrectomy for Terson syndrome. The purpose of study B was to determine the incidence and significance of vitreous hemorrhage in patients with subarachnoid hemorrhage. METHODS Study A is a retrospective review of case series. Study B is a prospective study. METHODS Study A examined a consecutive series of 4 children (7 eyes) and 23 adults (26 eyes). Study B examined a consecutive series of 100 patients. METHODS Subjects in study A underwent pars plana vitrectomy for dense vitreous hemorrhage following intracranial hemorrhage. In study B, ophthalmoscopic examination of patients undergoing neurosurgery for ruptured cerebral aneurysms was used. METHODS In study A, the extent and rapidity of visual recovery and intraoperative and postoperative complications were examined. In study B, the incidences of intraocular hemorrhage and Terson syndrome in the cohort and the significance of the presence of vitreous hemorrhage in patients with subarachnoid hemorrhage were examined. RESULTS Study A: There was substantial and rapid visual improvement in 25 of the 26 eyes (96%) of the adult patients, with 21 eyes (81%) achieving > or = 20/30 final visual acuity. Only limited improvement was achieved in children's eyes (< or = 20/60). Study B: Intraocular hemorrhage was found in 17% of eyes in patients with subarachnoid hemorrhage; the incidence of Terson syndrome was 8%. All patients with Terson syndrome and 89% of the patients with other types of intraocular hemorrhage had a history of coma compared with 46% of those without intraocular hemorrhage (P = 0.0003). CONCLUSIONS Vitreous hemorrhage in patients surviving subarachnoid hemorrhage appears to be more common than previously thought, underscoring the need for routine funduscopic screening. Surgical intervention is highly effective in hastening visual rehabilitation of adults with Terson syndrome. The less encouraging results in infants may be due to amblyopia or direct brain damage caused by the cerebrovascular incident.