Subependymomas are benign intraventricular tumors with an indolent growth pattern, which are usually asymptomatic, and most commonly occur in the fourth and lateral ventricles. When symptomatic, subependymomas often obstruct critical portions of the cerebrospinal fluid (CSF) pathway, causing hydrocephalus, and range from 3 cm to 5 cm in size. We report a case of an unusually massive subependymoma of the lateral ventricles treated with subtotal resection, ventriculoperitoneal shunt, and post-surgical radiation. The clinical course, radiographic and pathologic characteristics of this massive intraventricular subependymoma are discussed, as well as the differential diagnosis of lateral ventricular masses and a review of the literature concerning subependymomas.