Spontaneous necrosis of hepatocellular carcinoma (HCC) is rare and difficult to diagnose preoperatively if it occurs before the definitive diagnosis of HCC; this is because spontaneous necrosis of HCC exhibits various patterns in imaging studies. We compared imaging and pathological findings, and examined the possibility of diagnosing spontaneous necrosis of HCC using contrast-enhanced ultrasonography (CEUS). We experienced 2 cases of spontaneous necrosis of HCC. In case 1, spontaneous necrosis occurred after HCC diagnosis, while in case 2 it occurred before the first admission. The tumor in case 2 contained internal nodules and outer fibrous tissue. CEUS revealed a vascular spot in the hypovascular area during the vascular phase and a complete defect during the Kupffer phase. These findings accorded with the pathological findings and may be important for diagnosing spontaneous necrosis of HCC.