We evaluated the immunocytochemical expression of GPC3 in archival material obtained from fine needle aspiration of hepatic lesions to assess the sensitivity and specificity of this marker in cytological material and its potential diagnostic utility in differentiating hepatocellular carcinoma (HCC) from other primary benign or malignant hepatic tumors and from metastatic lesions in the liver. Forty-nine FNAs of the liver obtained between January 2000 and June 2006 were identified from our cytology files. Cytological diagnoses (confirmed by tissue diagnosis and/or clinical follow-up) included: 7 adenomas, 1 focal nodular hyperplasia (FNH), 24 HCCs, and 17 metastatic tumors. On the basis of the histological, clinical and/or radiological follow-up, 20 of 24 (83.3%) FNAs confirmed positive for HCC-expressed GPC3. All the seven adenomas and the only FNH were negative for GPC3. Sixteen out of seventeen metastatic malignancies were negative for GPC3. The only case expressing GPC3 was an anaplastic carcinoma with neuroendocrine features of unknown origin. In this study, the sensitivity of GPC3 in the diagnosis of HCC in the cytological material was 83.3%, the specificity 96%, the positive predictive value (PPV) 95% and negative predictive value (NPV) was 85.7%. Immunocytochemical staining for GPC3 in alcohol-fixed FNA material is a highly sensitive and specific method capable of distinguishing HCC from other benign and malignant hepatic lesions and from the great majority of metastatic lesions.