Proper treatment of congenital hypothyroidism warrants normal intellectual and physical development. This paper introduces the principles of treatment of congenital hypothyroidism, the recommended levothyroxine dosage, and the aims of therapy with its justification. The principles of treatment, specialist care of the patient, and methods used to evaluate therapeutic effects are described. Based on these data, recommendations concerning treatment and its monitoring in patients with congenital hypothyroidism are formulated. The paper also highlights the importance of educating the patients and/or their caretakers as one of the basic components of an effective therapy. The interpretation of screening tests in preterm neonates is provided as well. In the current screening program in preterm children TSH was determined between days three and five of life and then after three weeks. During this time TSH values are frequently low because of the immaturity of the hypothalamic-pituitary axis. Due to the increased risk of primary and secondary hypothyroidism in preterm and low birth weight babies the determination of TSH and fT4 between days three and five of life is recommended, irrespective of the screening test. (Endokrynol Pol 2016; 67 (5): 536–547)