Horner's Syndrome (ptosis, anisocoria, and anhydrosis) developed in a 22-year-old woman. A mediastinal mass was noted on chest x-ray. Further evaluation led to a diagnosis of Hodgkin's disease, nodular sclerosis type. Horner's syndrome is an unusual initial manifestation of Hodgkin's disease, and, in this case, it was due to oculosympathetic damage from mediastinal compression. Because the potential for cure is high in Hodgkin's disease, this diagnosis should be considered in patients presenting with Horner's syndrome.