Pituitary tumours are common and show a range of hormonal and proliferative behaviours that provide a model for the study of neoplasia mechanisms. Mutations in classic oncogenes and tumour-suppressor genes, however, are rarely associated with these tumours. In fact, most mechanisms of endocrine tumorigenesis differ significantly from those associated with haematological malignancies and non-endocrine tumours. Instead, tumorigenesis is promoted by hormones and growth factors that are implicated in pituitary development. Several mouse models have validated the roles of these alterations, although there are many differences in disease pathogenesis between mice and humans.