Aims. c-erbB-2 expression has been found to be an important prognostic parameter in various types of tumors, but the role played by this oncoprotein in thyroid tumors is still controversial. This study is designed to investigate c-erbB-2 expression in different types of thyroid tumors. Methods. c-erbB-2 protein over-expression was studied immunohistochemically (IHC) in 68 paraffin-embedded thyroid tumors (12 follicular adenomas, 20 papillary carcinomas, 20 follicular carcinomas, eight medullary carcinomas, eight anaplastic carcinomas), diagnosed at the Pathology Department of Cukurova University. Results. No expression of c-erbB-2 was found in anaplastic carcinomas, but 50% of the papillary carcinomas showed a cytoplasmic staining pattern and 45% had a mixed staining pattern (cytoplasmic and membranous patterns). Eight (40%) of the 20 follicular carcinomas showed a mixed cytoplasmic/membranous staining pattern and three (15%) showed only cytoplasmic reactivity. Cytoplasmic immunoreactivity was detectable for c-erbB-2 in six out of eight (75%) medullary carcinomas. Finally, seven cases of 12 (58%) follicular adenomas showed cytoplasmic staining. Conclusions. Investigation of the exact role of c-erbB-2 in thyroid tumors requires further studies, and the different patterns of immunostaining may be helpful for determination of prognosis as is the case in breast carcinoma.