[en] Pituitary adenomas are a common manifestation of multiple endocrine neoplasia type 1 (MEN1) but most of them occur sporadically. There are only a few well defined genetic abnormalities known to occur in these sporadic tumours. The MEN1 gene located on 11q13 has recently been cloned and allelic deletion and mutation analysis studies have implicated the MEN1 gene in a significant fraction of the sporadic counterparts of typical MEN1 neoplasms (parathyroid tumours, insulinomas and gastrinomas). To determine if MEN1 gene inactivation is also involved in the development of sporadic pituitary adenomas, allelic deletions of chromosome 11q13 and MEN1 gene mutations and polymorphisms were assessed in 35 sporadic tumours of the anterior pituitary (9 prolactin-secreting, 8 GH-secreting, 3 TSH-secreting, 2 TSH/GH-secreting, 4 Cushing, 9 silent). Thirty-one tumours were found to be heterozygous for at least one MEN1 intragenic polymorphism (25 cases) or for a flanking gene polymorphism (6 cases). The remaining tumours were not informative. No mutations were found in any tumour except in one prolactinoma which was homozygous or hemizygous for a mutation (1-117 C-->T) in a region close to the promoter. Unfortunately, blood or normal tissue was not available in this case. Our data show that somatic MEN1 mutations do not contribute significantly to tumorigenesis of sporadic pituitary adenomas and suggest that mutation of other genes are likely to contribute to the pathogenesis of these tumours.