Key PointsQuestionIs a family history of breast cancer (BC) associated with the prognosis of overall and estrogen receptor–specific BC?FindingsIn this cohort study of 28 649 female patients with BC in Sweden with up to 15 years of follow-up, having a family history of BC was associated with a lower risk of BC-specific death. This association was limited to the first 5 years after diagnosis and the estrogen receptor–negative subgroup and was not likely due to screening-associated early detection.MeaningThese findings suggest that patients with a family history of BC do not necessarily have worse outcomes, and some patients may have better outcomes, possibly due to enhanced motivation to receive and adhere to treatment.