Springer Science+Business Media B.V. 2007 Keywords BRCA1/2 Á Germ line mutations Á Sex ratio Á Hereditary breast/ovarian cancer Á Pakistan To the editor About 5% of breast cancers and 10% of ovarian cancers are a result of germ line mutations in the BRCA1 (MIM 113705) and BRCA2 (MIM 600185) genes [1, 2]. These genes encode multifunctional pro-teins that are involved in DNA repair, transcriptional regulation, and cell cycle/checkpoint control [3]. The underlying mechanisms by which BRCA mutations confer an increased susceptibility for the development of breast and ovarian cancer remain to be elucidated. There is evidence from recent publications that altered BRCA1/2 function may result in a skewed ratio of female to male births and a non-dominant transmission of mutant alleles to female offspring of BRCA muta-tion carriers [4–6]. However, these results are contro-versial since other studies have not supported these findings [7–14] and questions of ascertainment bias among tested families have been raised. Since all previous studies have been conducted in European and North-American populations, we analyzed the sex ratio in the offspring of BRCA mutation carriers from Pakistan.