Evidence of multiple endocrine neoplasia type 1 (MEN1) is found in approximately 2.7% of patients with pituitary adenomas. The multicentricity of pituitary adenomas has not yet been proved. Prolactinomas are most frequent in MEN1 pituitary tumors. Pituitary tumors with MEN1 are larger in size and more aggressive than without MEN1. Heterozygous germline mutations of MEN1 gene are responsible for MEN1 disorders. Various types of mutations likely causing loss of the gene function have been identified throughout the entire region in patients with MEN1 and related disorders. However, the function of menin, the product of MEN1 gene, remains to be established. Neither mutation hot spot nor phenotype-genotype correlation has been established in classical MEN1. A number of recent studies suggest that somatic mutations in the MEN1 gene do not play prominent role in the pathogenesis of sporadic forms of pituitary adenoma.