C-11 acetate positron emission tomography (PET) is known to have high sensitivity in detecting hepatocellular carcinoma. However, one of the shortcomings of C-11 acetate PET in the diagnosis of hepatocellular carcinoma is that C-11 acetate also accumulates in focal nodular hyperplasia, which makes it challenging to distinguish hepatocellular carcinoma form focal nodular hyperplasia when a conventional single time point PET imaging method is used. Two patients with suspected hepatocellular carcinoma and negative fluoro-deoxy-glucose PET scans underwent C-11 acetate PET dual time imaging in which both early and delayed images were acquired. One patient was subsequently confirmed having hepatocellular carcinoma while the other had focal nodular hyperplasia. C-11 acetate imaging was positive in both patients. Interestingly, in hepatocellular carcinoma the C-11 acetate activity in the delayed images is higher than in the early images while in focal nodular hyperplasia, the C-11 acetate activity decreased in the delayed image when compared with early images. Our findings suggest that dual time point imaging has potential to improve the diagnostic accuracy of C-11 acetate PET in the diagnosis of hepatocellular carcinoma.