Our work aims at defining by microarray gene expression profiles in different thyroid tumors: hyperfunctioning autonomous adenomas, and sporadic and post-Chernobyl papillary cancers. Gene expression analysis in hyperfunctioning autonomous adenomas allowed us to identify genes involved in various physiological processes of the thyroid. Concerning papillary cancers, gene expression profiling in post-Chernobyl and sporadic papillary carcinomas could not identify a specific gene expression signature allowing to distinguish both tumors although such a signature exists for autonomous adenomas and carcinomas. This suggests that both cancers represent the same disease, and that there is unlikely to be a molecular signature for radiation-induced thyroid cancer.