 Family health history, FHX, is an important factor in breast and ovarian cancer risk assessment. When used in a clinical setting, however, FHX is often incomplete or imprecise due to errors in reporting by patients. This can lead to incorrect risk classifications which could have serious implications for patient care. In order to address this issue, our study examined the effects of uncertainty in FHX on risk classification accuracy. We found that varying levels of uncertainty in FHX can significantly impact the accuracy of risk classification, with some models being as much as 64% off the mark. Therefore, it is essential that uncertainty in FHX be taken into account when developing and implementing risk prediction models in clinical settings. This article was authored by Lance T. Fleger, Clinton C. Mason, and Julio C. Faceli.