PurposeTo present four patients with invasive prolactin-secreting pituitary adenomas extending in the orbit.MethodsRetrospective, noncomparative case series.ResultsIn all cases, the tumor was a large, invasive prolactin-secreting adenoma. In three cases, significant permanent vision loss occurred and severe disfigurement resulted; two of these patients died of tumor-related complications. In one case, the tumor responded well to medical treatment, and the orbital symptoms improved significantly.ConclusionAlthough it is rare for a pituitary adenoma to invade the orbit, devastating consequences to the integrity of the globe and ocular adnexa may result. Therefore, early recognition and proper treatment of orbital pituitary tumors are of utmost importance to minimize ocular and orbital damage.