RELATO DE CASOCopyright Pisani et al. Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. AbstractCanine congenital hypothyroidism is a rare and underdiagnosed endocrine disorder, their true incidence is unknown because many dogs with this condition die before reaching three months of age. The disorder can cause a range of clinical signs as the lack of thyroid hormones on the animal's body because of low metabolism signs of multiple organs. Affected dogs may have mental retardation and abnormalities in skeletal development. Diagnosis is made through the animal's history, laboratory screening tests added to the clinical and epidemiological findings and serum levels of thyroid hormones. This paper reports a case of canine congenital hypothyroidism in a Chow-Chow dog, with one year old, diagnosed at the Veterinary Hospital of the Federal Rural University of Rio de Janeiro. The animal was submitted to hormone replacement therapy with levothyroxine Sodium resulting in clinical improvement.