Pourfour du Petit Syndrome (PdPS) is characterized by signs of oculosympathetic hyperactivity caused by irritation in the oculosympathetic pathway and shares etiologies with Horner Syndrome. We present the case of a 64-year-old woman with Pourfour du Petit syndrome due to compression of the second-order cervical sympathetic chain neuron from a dominant and prominent right internal jugular vein compensatory for contralateral agenesis. Internal jugular vein agenesis is a rare developmental vascular anomaly and is asymptomatic in the majority of patients with this condition.