Several studies have shown that glypican 3 (GPC3) could be a useful diagnostic marker for hepatocellular carcinoma (HCC) and for differentiating HCC from nonneoplastic and preneoplastic liver disease. To systematically investigate the epidemiology of GPC3 expression in the liver and in other organs and tissues, we used tissue microarray technology comprising 4,387 tissue samples from 139 tumor categories and 36 nonneoplastic and preneoplastic tissue types. The immunohistochemical expression of GPC3 was assessed semiquantitatively using a 10% cutoff score and was detected in 9.2% of nonneoplastic liver samples (11/119), 16% of preneoplastic nodular liver lesions (6/38), and 63.6% of HCCs (140/220), underlining the role of GPC3 in hepatocarcinogenesis. Furthermore, several other tumors revealed consistent expression of GPC3, including squamous cell carcinoma of the lung (27/50 [54%]), testicular nonseminomatous germ cell tumors (32/62 [52%]), and liposarcoma (15/29 [52%]).