A 79-year-old woman presented with abdominal pain. Ultrasound revealed an intra-abdominal mass in the left renal region. Comprehensive endocrine workup was unremarkable. The patient was referred for further diagnostic workup. FDG PET/CT revealed a hypermetabolic mass in the left adrenal region. In addition, pathologically increased tracer uptake of 2 renal veins (the upper vein crossing in front of the aorta the lower one crossing behind the aorta) and the inferior vena cava raised the concern for malignant venous infiltration. Adrenalectomy, nephrectomy, and thrombectomy were carefully planned and performed. Adrenocortical carcinoma with tumor thrombus and caval extension was proven by histopathology.