We report a novel BRCA1 germline 4156delAA mutation detected in a 41-year-old woman with breast and ovarian cancer. Genomic DNA was obtained from peripheral blood. Standard polymerase chain reactions and direct sequencing were performed. This mutation originates a premature stop at codon 1354 of BRCA1 protein and has not been documented in any published report to the best of our knowledge. The mutation was not observed in any other family studied. Since this novel mutation was associated with both breast and ovarian cancer, the genotype-phenotype correlation was investigated in a patient base of 30 families.