Nevoid basal cell carcinoma syndrome (NBCCS; basal cell nevus syndrome or Gorlin syndrome) is a cancer-predisposition syndrome characterized by multiple basal cell carcinomas (BCCs) and diverse developmental defects. The gene for NBCCS has been mapped to 9q23.1-q31 in North American and European families. In addition, loss of heterozygosity (LOH) for genetic markers in this region has been detected in sporadic BCCs, indicating that the NBCCS gene is probably a tumor-suppressor gene. In this study we have determined that the NBCCS gene is also linked to this region in Australasian pedigrees and that there is no significant evidence of heterogeneity. We have defined the localization of the gene by multipoint and haplotype analysis of 15 families, using four microsatellite markers. LOH at these loci was detected in 50% of sporadic BCCs, a rate that is significantly higher than that in other skin lesions used as controls.