ABSTRACT. Peixoto P.V., Ramadinha R.R., Donatti F.C., Teixeira R.S., Azevedo-Meleiro C.H., França T.N., Malafaia P.A.M. & Miekeley N.F. [Considerations about the levels of iodine in the diet and the occurrence of hypothyroidism in dogs and humans in the State of Rio de Janeiro, Brazil]. Considerações sobre os teores de iodo na dieta e ocorrência de hipotireoidismo em cães e humanos. Revista Brasileira de Medicina Veterinária, 34(3):223-229, 20l2. Departamento de Nutrição Animal e Pastagem, Instituto de Zootecnia, Universidade Federal Rural do Rio de Janeiro, BR 465 Km7, Seropédica, RJ 23890-000, Brasil. E-mail: firstname.lastname@example.org Considering that dietary iodine deficiency or excess are capable to induce hypothyroidism animals, and that there is a high incidence of the condition in dogs in the State of Rio de Janeiro, the aim was to verify by chemical analysis of dry dog foods and commercial salts for human consumption, if the imbalance in the levels of this element can be associated with the occurrence of this condition. Our data show that some brands of dog food contain excess of iodine while others are highly deficient of this element, indicating that the disequilibrium may be the cause of the problem. Our study demonstrates also the urgent need for more comprehensive investigation capable of measuring the extension of the problem in dogs. Furthermore, the correlation between the mean daily ingestion of salt by humans (15g/day) and the elevated concentrations of iodine in some table salt brands (sodium chloride), sold in the state of Rio de Janeiro, also suggests that the excess of iodine can be, at least partly, responsible for the high incidence of hypothyroidism in humans in this country, as supported by some and denied by other researchers that have been recently studying the problem.