A 52-year-old man without known medical history presented with painful, progressive, bilateral lower extremity edema over a two-week period. An abdominal exam noted a firm left upper quadrant mass. Emergency department (ED) point-of-care ultrasound (POCUS) revealed a hyperechoic, heterogeneous structure in the inferior vena cava that was determined to represent a tumor thrombus extending from a primary renal cell carcinoma. This case demonstrates how POCUS was valuable in rapidly diagnosing this rare cause of lower extremity edema and its usefulness in directing the initial ED management of this patient.