The purpose of this study was to assess the relationship between the clinical findings before starting treatment and the development quotient in children treated for congenital hypothyroidism. Patients with congenital hypothyroidism (n = 129) were divided into favorable and unfavorable groups according to intellectual performance. Children with congenital hypothyroidism generally have a similar intellectual outcome to that of healthy children. However, a low birth weight, the presence of complications, and a high serum thyroid-stimulating hormone value are the risk factors for unfavorable cases, who consistently have a development quotient score of less than 100.