The human calcitonin receptor (CTR) is a transmembrane peptide with dual action as a receptor for the hormone calcitonin and as an extracellular calcium sensor. Therefore, CTR dysfunction could lead to disorders of calcium metabolism associated with hypercalcemia, such as the Williams syndrome (WS). WS is a developmental disorder caused by a deletion at chromosome 7q11.23 that includes the elastin locus (ELN). We have mapped the CTR gene (CALCR) to chromosome band 7q21.3 by polymerase chain reaction and single-strand conformation analysis of somatic cell hybrids as well as fluorescence in situ hybridization (FISH) to metaphase chromosome spreads. Two-color FISH cohybridizing CTR and ELN probes confirmed that CALCR maps telomeric to ELN. Subsequent analysis of chromosome spreads from four WS patients revealed deletion of the ELN locus in all of them and normal hybridization of CTR probes to both chromosome 7 homologues, indicating that CALCR lies outside the deleted region.