Multiple endocrine neoplasia types 2A and 2B (MEN 2A and MEN 2B) and familial medullary thyroid carcinoma (FMTC) are dominantly inherited cancers that have in common the clinical feature of medullary thyroid carcinoma (MTC). We have performed both genomic long-range restriction mapping and yeast artificial chromosome (YAC) contig assembly and restriction mapping to establish physical linkage, order, and distances between six loci in 10q11.2 near the genes responsible for these hereditary cancers. RET, D10S94, D10S182, and D10S102 have been mapped in genomic DNA. RET, D10S94, D10S182, D10F38S3, and the 10q11.2 sequences detected by DNA marker DM124 are encompassed by a 1-Mb YAC contig. Six physically linked loci are within 1.4 Mb and have an order and orientation of 10cen, D10F38S3, DM124, RET, D10S94, D10S182, D10S102, 10qter. Mutations in the RET proto-oncogene have recently been demonstrated to be associated with MEN 2A and FMTC. RET is located within a genetically defined MEN2A candidate interval between D10S141 and D10S94; MEN2B has been mapped to a larger, overlapping region between D10S141 and a more distal locus, RBP3. Both our genomic physical map and our YAC contig span the entire MEN2A candidate region and overlap with that of MEN2B. These maps will facilitate the identification of genes that can be considered candidates for MEN2B and the identification of tumor-specific alterations important in sporadic MTC.