A deleted genomic region including the MEN1 gene was determined in a family with multiple endocrine neoplasia type 1 caused by a large germline deletion. Gene dose mapping by the modified gene dose assay technique roughly located the deletion end points, which were then precisely determined by nucleotide sequencing. The deletion was approximately 68 kbp flanked by a 3-base pair repeat and included the whole MEN1, MAP4K2 and KAPPA-200 genes. This is the first case of a large germline deletion responsible for multiple endocrine neoplasia type 1, in which the size and end points were determined precisely. (C) 2003 Elsevier Ireland Ltd. All rights reserved.