The physiological and developmental effects of thyroid hormones are mainly due to the control of gene expression after interaction of T-3 with the nuclear receptors. To understand the role of thyroid hormones on cerebral cortex development, knowledge of the genes regulated by T-3 during specific stages of development is required. In our laboratory, we previously identified genes regulated by T-3 in primary cerebrocortical cells in culture. By comparing these data with transcriptomics of purified cell types from the developing cortex, the cellular targets of T-3 can be identified. In addition, many of the genes regulated transcriptionally by T-3 have defined roles in cortex development, from which the role of T-3 can be derived. This review analyzes the specific roles of T-3-regulated genes in the different stages of cortex development within the physiological frame of the developmental changes of thyroid hormones and receptor concentrations in the human cerebral cortex during fetal development. These data indicate an increase in the sensitivity to T-3 during the second trimester of fetal development. The main cellular targets of T-3 appear to be the Cajal-Retzius and the subplate neurons. On the other hand, T-3 regulates transcriptionally genes encoding extracellular matrix proteins, involved in cell migration and the control of diverse signaling pathways.