The nevoid basal cell carcinoma syndrome is an autosomal dominant disorder, characterized by predisposition to multiple early basal cell carcinomas of the skin and several other tumours as well as frequent occurrence of developmental anomalies. The gene has previously been mapped to chromosome 9q22 and is believed to function as a tumour suppressor. We have applied linkage and haplotype analysis to four Swedish nevoid basal cell carcinoma syndrome families to refine the localization of the nevoid basal cell carcinoma syndrome gene. Information from critical recombinants localizes the gene proximal of marker D9S287, which in combination with analysis of loss of heterozygosity in a hereditary cardiac fibroma has allowed us to define a minimal candidate region of 1Mb or less for the nevoid basal cell carcinoma gene flanked by the markers D9S280 and D9S287 in the 9q22.3 area.