This short review will focus on the mechanisms which are thought to be directly involved in GH expression and particularly on the monogenetic disorders which were shown to cause isolated growth hormone deficiency (IGHD) due to insufficient expression of GH. The overwhelming majority of genetic defects detected in isolated growth hormone deficiency (IGHD) are mutations of the coding region of the GH-1 gene which belongs to a five genes containing gene cluster located on 17q22–24. Depending on the type of the GH-1 gene mutation, the mode of inheritance is recessive or dominant. The promotor region of the GH-1 gene which encompasses the 300 bp of the 5′ flanking region is highly polymorphic, but the functionally important cis-acting elements are conserved. This sequence is sufficient to control GH expression in cultured cells, but not in transgenic mice: the human GH locus control region, an enhancer region of the GH-1 gene located approximately 15–32 kB upstream of the GH-1 coding region was shown to direct pituitary-specific, high-level GH expression in vivo. Promotion of the GH expression needs the coordinate binding of pituitary-specific (i.e., POU1F1) and ubiquitous trans-acting factors to the cis-acting elements. The mutational analysis of trans-acting factors and cis-acting elements of the GH-1 gene has so far not established any defect outside the coding region as the genetic basis of IGHD except for POU1F1 mutations which cause multiple pituitary hormone deficiency including GHD. Several mutations of the GHRH-receptor gene were shown to result in severe IGHD. In the future, the discovery of new defects of the GH expression machinery will add to our understanding of how GH is sufficiently supplied to the organism and will hopefully simplify and improve the diagnostic approach in a subset of children with IGHD.