A 48-year-old woman presented with a 1-year history of an enlarging, nontender right lateral intrapalpebral mass overlying the insertion of the right lateral rectus muscle, associated with a 3-month history of worsening right orbital pain and retrobulbar headaches. MR imaging revealed an isointense right orbital mass contained entirely within the right lateral rectus muscle and indistinguishable from it. Transconjunctival biopsy established the diagnosis of lymphangioma. To the authors' knowledge, this case represents the first reported orbital lymphangioma contained entirely within an extraocular muscle.