The causal role of Epstein-Barr virus (EBV) in the development of B-cell lymphoma, especially in immunocompromised individuals, has been suggested. The purpose of the present study was to evaluate an association of EBV with thyroid lymphoma (TL) and chronic lymphocytic thyroiditis (CLTH) which is known to play an important role in the development of TL. Thirty cases with TL and 28 with CLTH were studied for presence or absence of EBV genome in the lesions using the polymerase chain reaction (PCR) and the in situ hybridization method. EBV genomes were detected by PCR in one and two cases with CLTH and TL, respectively. Subtyping of EBV genome was possible in one TL case showing B-type in EBNA-2 coding region. In situ hybridization revealed positive signals in the nucleus of lymphoma cells, which also expressed latent membrane protein-1. The present findings indicate that activation of EBV in TL is not common.