Several patients with pituitary dwarfism and a variable degree of hypothyroidism have been shown to have mutations in their Pit-1 gene. Pit-1 activates transcription of the growth hormone and prolactin genes and is necessary for the control of the beta-TSH gene transcription. The various mutations have different effects on the DNA binding and transactivating properties of Pit-1. Multiple pituitary hormone deficiency due to Pit-1 mutations is inherited either dominantly or recessively depending on the DNA binding properties of the mutant protein. The comparison of pheno- and genotype in patients with multiple pituitary hormone deficiency provides some insight into the function of the Pit-1 protein.