Fanconi anemia (FA) is a rare autosomal recessive cancer susceptibility disorder characterized by cellular hypersensitivity to mitomycin C (MMC). Six FA genes have been cloned, but the gene or genes corresponding to FA subtypes B and D1 remain unidentified. Here we show that cell lines derived from FA-B and FA-D1 patients have biallelic mutations in BRCA2 and express truncated BRCA2 proteins. Functional complementation of FA-D1 fibroblasts with wild-typeBRCA2 complementary DNA restores MMC resistance. Our results link the six cloned FA genes with BRCA1 and BRCA2in a common pathway. Germ-line mutation of genes in this pathway may result in cancer risks similar to those observed in families withBRCA1 or BRCA2 mutations.