Transesophageal echocardiography (TEE) is sometimes used in renal cell carcinoma excision for evaluating the extension of tumor in the inferior vena cava (IVC), characterizing the tumor anatomy, monitoring the tumor during surgical mobilization, and assessing cardiac function. Although the risk for embolization is small, when embolization does occur, its consequences can be catastrophic. In this case report, we describe the crucial role of TEE in diagnosing an intraoperative migratory embolus from the IVC to the pulmonary artery and also provide both single-frame photographs and Internet-accessible videos of the event. Our case illustrates the key role that TEE played in the intraoperative management of a patient with renal cell carcinoma undergoing surgical excision of tumor. TEE aided in accurately defining the cephalad extent of the thrombus, provided continuous monitoring of the thrombus during surgical manipulation, and allowed immediate identification of its embolization and proper notification of the surgeons. This case illustrates the crucial role TEE played in the management of a migratory tumor embolus and argues for its routine use during excision of renal cell carcinomas invading the IVC.