Adherence to mammographic screening recommendations following BRCA1/2 testing is generally assessed through self-reports. However, the validity of self-reported mammography by women who had undergone BRCA1/2 genetic testing is still unknown. This study aimed to assess the validity of self-reported mammography use in the past 12 months among women who had undergone BRCA1/2 testing. Using a self-administered questionnaire, 307 women who never had cancer were asked 1 year following BRCA1/2 test result disclosure whether they undergone a mammography in the past 12 months. For each participant, this information was compared to that provided by the Quebec Health Insurance Board administrative data set for mammography claims during the same period, here considered as the gold standard. Sensitivity (Sn), specificity (Sp), predictive values, and Cohen's kappa (κ) were calculated. The robustness of these estimates was assessed using sensitivity analysis in which we varied the administrative data time lapses up to 18 months. Overall, the agreement between self-reports and administrative data was 88% (κ = 0.74). Among the 180 participants who had a mammography according to the administrative data, 172 adequately reported this information (Sn = 96%). Sp was moderate (76%), meaning that 24% of those who did not have a mammography reported one. Extending the time lapses to 18 months increased the Sp substantially (Sp = 90%). Self-report overestimates the use of mammography, mainly because women tend to minimize the elapsed time since their last mammography. Self-reports should be used cautiously to assess adherence to mammographic screening following BRCA1/2 testing.