BACKGROUND Several studies conclude that small for gestational age (SGA) children have a higher number of comorbidities, as well as a different hormonal profile compared to those with appropriate weight for gestational age (AGA). Thyroid hormones play an important role in growth and neurocognitive development. Thyroid function in SGA children is still not completely known. OBJECTIVE To compare the thyroid function of SGA children during the first 2 years of life with that in publications on thyroid function in other groups of infants, such as AGA and premature children, using the same methodology. METHODS A cohort of 38 SGA children was obtained, in which the thyrotropin (TSH) values in blood were measured at different points in the development of the SGA child. The results were compared with a population of AGA children from Zaragoza and a population of premature children from Barcelona by comparing the means using a 2-tailed test. RESULTS A statistically significant difference (P < 0.05) was observed between the SGA children in our study and the AGA children older than 6 months, but not between the SGA children of the study and the population of premature infants. CONCLUSIONS SGA children have higher TSH values compared to AGA children older than 6 months. Therefore, it seems reasonable to establish a screening and a follow-up protocol in those SGA with high risk to develop thyroid dysfunction.