The impact of treatment on subsequent fertility and the safety of childbearing are major complicating factors for young women diagnosed with breast cancer. As national data indicate women are postponing first pregnancy to older ages; therefore, many young patients are seeking clinical guidance regarding the safety of conception and treatment options that may not prevent subsequent pregnancy. Newly developed chemotherapy protocols of brief duration have improved life expectancy enabling some women to consider childbearing. This study was conducted to compare prognosis among breast cancer patients with and without a subsequent pregnancy. Medical record review of female members of a Northern California prepaid health care plan enabled the identification of 107 women with one or more subsequent pregnancies and 344 cases without a pregnancy, who were diagnosed between 1968 and 1995. Sets were matched on age, year and stage at diagnosis, months of survival and recurrence status at conception. Among the matched sets, neither risk of recurrence nor death differed significantly by subsequent pregnancy history during an average 12 years of follow-up (adjusted hazard ratio [HR] recurrence: 1.2 [0.8, 2.0]; adjusted HR death: 1.0 [0.6, 1.9]). Women interested in preserving their fertility and considering pregnancy are a self-selected population; therefore, to reduce potential bias, cases were matched on recurrence status at time of conception. Although the number of cases was limited, subgroup analyzes indicated a small, nonsignificant adverse effect among women who conceived within 12 months of diagnosis. This analysis of carefully matched cases provides reassurance that long-term prognosis was not adversely affected by subsequent pregnancy.