We examined the relationship between the survival of women with breast cancer and the gender of their first children using a genealogy-based survival analysis. The study group consisted of 2,155 parous women diagnosed in Utah (United States) with first primary breast cancers (excluding in situ tumors). We calculated hazard rate ratios (HRR) which were adjusted for stage, median survival times, and proportions surviving for three-, five-, and 10-year intervals stratified by age at diagnosis. Median survival among women diagnosed under the age of 45 was 171 months if the first child was female, but only 66 months if the first child was male (HRR = 1.66, 95 percent confidence interval = 1.07-2.57, for male children). For women diagnosed at age 45 or older, all survival times were similar, although women whose first child was male had slightly longer median survival time. These findings suggest that the gender of the first child has a strong influence on survival among women diagnosed under 45 years of age, but not among those diagnosed later in life. Gender of the first offspring may be a useful clinical indicator of prognosis and survival and may provide insights into etiologic and promotional factors for breast cancer.