Objectives: We assessed accuracy of self-reported lifetime mammography history by BRCA1/2 mutation carriers with and without breast cancer. Study Design and Setting: Within the framework of the HEBON study (The Netherlands Collaborative Group on Hereditary Breast Cancer), 218 Dutch BRCA1/2 mutation carriers had completed a risk factor questionnaire between 2006 and 2007. Accuracy of self-reported lifetime mammography history was assessed by medical record review and calculated by proportion agreement and Cohen's kappa coefficient (kappa). Results: For 177 (81%) carriers, validation could be completed. Accuracy of reporting of ever/never exposure was excellent (i.e., agreement >= 93%, kappa >= 0.81) for all time frames (lifetime, before age 30, and at ages 30-39). Accuracy of age at first mammogram was poor to moderate (i.e., 39%, kappa = 0.37) for exact agreement and improved to almost excellent (i.e., 70%, kappa = 0.69) for agreement within I year, indicating that differences were small. Although cases more often tended to underestimate their exact age at first mammogram, whereas unaffected carriers tended to overestimate, this difference in the direction of inaccuracy was not statistically significant (P = 0.237). Accuracy of age at last mammogram was moderate and improved to excellent for agreement within 1 year. Carriers tended to underreport the time since last mammogram ("telescoping") and overreported the number of mammograms. Conclusion: Accuracy of self-reported lifetime mammography history in carriers highly varied, depending on the measure under investigation. However, the extent of the observed misclassification was small and mostly nondifferential. (C) 2011 Elsevier Inc. All rights reserved.