Background. Identification by medical providers of families at higher risks for breast cancer relies on patients’ recollection of family histories. While patients seem to report the occurrences of breast cancer in their first‐degree relatives accurately, little is known about the precision of reports of ages at diagnosis of cancers in relatives, one of the most revealing clues with regard to hereditary transmission. Moreover, the methods used in previous studies to elicit the family reports render their applicability to the medical setting questionable. Methods. Confirmatory pathology records were sought and compared with reports of breast cancer events among 125 first‐degree relatives by 68 women with breast cancer and 37 women without the disease. Results. Sixty‐seven (90.5%) of the reports of the occurrence of breast cancer in relatives by affected women and 32 (97.0%) of those by unaffected women were accurate. Women reporting several affected relatives often overreported the presence of breast cancer events. Nearly 89% of the reports of age at diagnosis were correct within five years. The average error in the reports was 2.0 years. The precision of reports of age at diagnosis did not differ according to the educational level of the proband, the age at which the relative had been diagnosed, or the type of relative affected. However, the mean error in reporting the age at diagnosis of relatives was significantly larger among probands 70 years old or older compared with younger probands. Conclusions. These results suggest that relying on reports by patients with and without breast cancer should not critically affect the assessment of breast‐cancer risks for family members. Nevertheless, verification by examination of pathology records is justified when decisions about patient management and referral for genetic counseling are made based on reports of several affected relatives.