Viral infections are frequently cited as a major environmental factor involved 
in subacute thyroiditis and autoimmune thyroid diseases This review examines the 
data related to the role of viruses in the development of thyroiditis. Our 
research has been focused on human data. We have reviewed virological data for 
each type of thyroiditis at different levels of evidence; epidemiological data, 
serological data or research on circulating viruses, direct evidence of thyroid 
tissue infection. Interpretation of epidemiological and serological data must be 
cautious as they don't prove that this pathogen is responsible for the disease. 
However, direct evidence of the presence of viruses or their components in the 
organ are available for retroviruses (HFV) and mumps in subacute thyroiditis, 
for retroviruses (HTLV-1, HFV, HIV and SV40) in Graves's disease and for HTLV-1, 
enterovirus, rubella, mumps virus, HSV, EBV and parvovirus in Hashimoto's 
thyroiditis. However, it remains to determine whether they are responsible for 
thyroid diseases or whether they are just innocent bystanders. Further studies 
are needed to clarify the relationship between viruses and thyroid diseases, in 
order to develop new strategies for prevention and/or treatment.