Background: Neonatal hypothyroidism is a serious endocrinal disorder that must be diagnosed promptly to avoid irreversible neurological deficits. Aim of work: screening of all preterm infants for thyroid dysfunction. Patients and methods: All preterm infants enrolled to this study were subjected to thorough history taking and complete physical examinations. Investigations: initially screening for hypothyroidism was done according to Egyptian screening program and serum TSH, T4, and free T4 were done within the 1st week of life and repeated at the end of 2nd and 4th week of life for those with abnormal results only. Results: Abnormal thyroid function was detected in 178 (50%) preterm infants.Twenty-two infants were excluded from the study. Mean serum levels of TSH, T4 and free T4 were higher among group II infants (more mature) than 1st group (less mature). The mean levels of T4 and free T4 were higher at the end of 4th week of life than their levels during the 1st week of life. Transient hypothyroxinemia was more frequent thyroid dysfunction disorders among both groups (52.5 % and 38 % for 1st and 2nd groups respectively). Neonatal hypothyroidism, transient primary neonatal hypothyroidism, and transient hyperthyrotropinemia were detected in 9 (11.25%), 18 (22.5%), and 11 neonates (13.75%), respectively for the 1st group and observed in 7 (9.2%), 14 (18.4%), and 9 neonates (11.8%), respectively for the second group Conclusions: Thyroid dysfunction was moderately common among preterm neonates. Protocol for thyroid function tests among preterm infants is essential.