Molecular studies on pituitary adenomas support a major role of molecular alterations in the pathogenesis of pituitary adenomas. Nevertheless, alterations in the neuro-hormonal control of the pituitary could also be involved in pituitary tumors formation. The finding that most pituitary adenomas are monoclonal has stimulated a search for somatic mutations. For instance, activating mutations of the Gs protein, leading to constitutive stimulation of the cAMP pathway, have been found in a subset of GH-secreting adenomas. But GHRH (growth hormone-releasing hormone) tumoral hypersecretion also stimulates the cAMP pathway and causes acromegaly. Pituitary tumor formation might result from accumulation of several alterations that would determine the tumoral phenotype. The majority of these alterations remains to be found.