Multiple endocrine neoplasia type 1 (MEN-1) is characterized by hyperfunction and tumor formation of the parathyroids, anterior pituitary and endocrine pancreas. We carried out exon-specific, PCR-based DNA sequencing of the coding exons of the MEN1 gene in 8 Israeli MEN1 patients: 4 familial and 4 sporadic. We similarly analyzed Israeli families with a unique phenotype of isolated hyperprolactinemia (HPRL). Four mutations were detected in 4 MEN1 patients: C to T alteration at nucleotide 2608 resulting in R108X, and three intronic insertions/deletions (a 13 basepair (bp) deletion and a 1 bp insertion both in intron 1, and a 2 bp insertion in intron 3) leading to exonic frame shifts as they encompass the splice junctions. An additional patient exhibited a compound mutation: a G to T change at position 7614 resulting in E463X, and insertion/deletion of 9 bp at position 7622-7630 resulting in EAE466-468X. Haplotype analysis showed no segregation of phenotype with 11q13 markers in 4 familial HPRL, and no men 1 germline mutations were detected in three representative individuals, from 3 families. Our results confirm that men 1 gene germline mutations occur in the majority of patients with clinically diagnosed MEN1, and that familial HPRL is a genetically distinct disorder.