Iatrogenic pneumothorax secondary to thoracentesis is relatively uncommon but does present to the emergency department (ED). Iatrogenic pneumothoraces developing tension physiology are rare. We report a case of an elderly female patient presenting to the ED with an isolated chief complaint of bilateral leg swelling, beginning the day after a thoracentesis, which was performed 3 days prior for pleural effusions secondary to lung cancer. Given that the patient was hemodynamically stable, not hypoxic, and had a history of chronic obstructive pulmonary disease and recent history of pleural effusions with diminished lung sounds throughout, this was a radiologic diagnosis. Immediately upon diagnosis, a 10F intrapleural catheter was inserted at the second intercostal space in the midclavicular line with successful resolution of the tension phenomenon. The patient tolerated the procedure well, and the catheter was removed on hospital day 2 without recurrence of the pneumothorax. She experienced resolution of her lower extremity swelling and was discharged from the hospital 2 days later. Isolated inferior vena cava syndrome secondary to a subacute tension pneumothorax was likely the cause of the patient's symptoms. This presentation is very rare and is undocumented in the literature. A high degree of suspicion for acute chest pathology should exist in every patient presenting to the ED with history of recent pleural violation.