In newborns, congenital hypothyroidism occurs due to complete absence or underdevelopment of the thyroid gland, or if the thyroid gland is present but does not produce normal thyroid hormones. It is important for parents to pay attention to the fact that children with hypothyroidism can suffer from mental retardation and significant growth failure in the future. Most children with hypothyroidism have atypical clinical manifestations at birth, initially with no symptoms, but later with lethargy, loss of appetite, low muscle tone, constipation, hoarseness, and a mass formed by the abdominal contents protruding from the abdominal wall at the umbilical cord (umbilical hernia). If left undetected, undiagnosed, and untreated, hypothyroid children may develop growth retardation, mental retardation, and short stature, and eventually the infant may develop rough facial features and an enlarged tongue. Blood tests for thyroid hormone levels in children will reveal elevated thyrotropic hormones and decreased thyroid hormones. In children with a clear diagnosis of hypothyroidism, immediate treatment with levothyroxine sodium is administered at an initial dose of 4-6 μg/kg/day for 4 weeks, followed by a serum thyroid function review, after which the drug dosage is adjusted according to the results of the review. If thyrotropin levels do not decrease significantly, the dose is too low and should be increased; if thyrotropin levels are below normal and serum free thyroxine levels are elevated, the dose is too high and should be reduced. During the treatment period, the physical and intellectual development of the child should be observed and ultrasound examination of the thyroid gland should be performed. If the thyroid gland development, intelligence and physical development are normal, the medication should be discontinued for observation and serum thyroid function should be rechecked one month after discontinuation. In cases of abnormal thyroid development, lifelong treatment is required. If compression of the trachea and swallowing dysfunction are found, they can be treated surgically. If treatment is started within the first 3 months of life, the majority of intelligence can be normalized.