Congenital Hypothyroidism affects between 1:3000 and 1:4000 newborn infants in iodine-sufficient regions. Some studies have shown that mutations and polymorphisms in the TSH receptor gene are responsible for this disease. In the present study, mutations of exon 10 of the TSH receptor gene were investigated in Congenital Hypothyroidism patients. In the present study a sample of 90 Brazilian patients with primary congenital hypothyroidism was analyzed. Genomic DNA was isolated from peripheric blood samples. Exon 10 of the TSH receptor gene was amplified by PCR, and amplicons were automatically sequenced. Three nucleotide alterations were identified: c.1377G>A (A459A), c.1935G>A (L645L), and c.2181C>G (D727E). A459A polymorphism was also described previously in patients with thyroid cancer. The nucleotide alteration L645L was found in a single patient. This is the first time the L645L mutation has been described. D727E polymorphism showed high frequency (allele frequency 10%) in present study when compared to others reports.