A four-year-old previously well boy collapsed unexpectedly and was taken immediately to hospital, where he developed seizures and cardiogenic shock with lethal, rapidly progressing multi-organ failure. At autopsy, the height was >90th percentile and there were indications of early virilization. Internally, a friable tumor of the left adrenal gland was identified that had invaded the left renal vein and inferior vena cava. Histology revealed typical features of an adrenocortical carcinoma with aggregated trabeculae of cells containing abundant eosinophilic cytoplasm and large pleomorphic nuclei. There was strong positive cytoplasmic staining for inhibin; mitochondria were shown on electron microscopy to contain prominent electron-dense granules. Death was due to massive pulmonary tumor embolism. Although adrenocortical carcinomas are very rare and are more commonly found in adults, the current case demonstrates that they may also occur in childhood and be responsible for unexpected death by the very unusual mechanism of tumor embolism.