Histologic examination of ten intraocular melanomas (eight choroidal and two of the iris and ciliary body) with dispersion of tumor cells into the vitreous body showed optic nerve invasion ranging from only a few collections of tumor cells lying in the anterior portion of the nerve, to invasion of the entire nerve and possibly the chiasm. Nine of the ten melanomas were partially necrotic. Orbital recurrence developed in four cases in which the tumors extended to the surgically cut margin of the excised optic nerve. All of the eyes had no light perception and had angle-closure glaucoma. In a companion retrospective study of 38 endophytic retinoblastomas with optic nerve invasion, 29 had angle-closure glaucoma. The posterior dispersion of tumor cells, and possibly their optic nerve head invasion, may have been enhanced by the obstruction of the normal anterior segment aqueous outflow channels and the associated glaucoma.