Morphologic differentiation of clear cell hepatocellular carcinoma (HCC-CC) from clear cell renal carcinoma (RCC-CC) may not be possible without the aid of immunohistochemical stains. We performed a battery of immunohistochemical stains on 10 previously diagnosed HCC-CCs, and 10 RCC-CCs, in order to determine which single or combination of immunostains would be most useful in diagnosis. We concluded that a positive Hepatocyte immunostain (DAKO) is sufficient for a diagnosis of HCC-CC if enough tissue is available. This immunostain distinguishes HCC-CC from other clear cell malignancies with sensitivity of 90% and specificity of 100%, when biopsy material is adequate. Other tests were much less sensitive, although several had specificity of 100%. A negative immunostain does not exclude the diagnosis of HCC-CC (negative predictive value 91%, especially in small biopsy material) and should be followed by additional immunostains such as pCEA for demonstration of tumor canaliculi, ubiquitin for Mallory bodies, and several epithelial cell markers that are typically positive in RCC-CC (epithelial membrane antigen, Leu M-1, pancytokeratin) and negative in HCC-CC.