Obtaining complete medical record information can be challenging and expensive in breast cancer studies. The current literature is limited with respect to the accuracy of self-report and factors that may influence this. We assessed the agreement between self-reported and medical record breast cancer information among women from the Ontario site of the Breast Cancer Family Registry. Women aged 20-69 years diagnosed with incident breast cancer 1996-1998 were identified from the Ontario Cancer Registry, sampled on age and family history. We calculated kappa statistics, proportion correct, sensitivity, specificity, and positive and negative predictive values and conducted unconditional logistic regression to examine whether characteristics of the women influenced agreement. The proportions of women who correctly reported having received a broad category of therapy (hormone therapy, chemotherapy, radiation, or surgery) as well as sensitivity and specificity were above 90%, and the kappa statistics were above 0.80. The specific type of hormonal or chemotherapy was reported with low-to-moderate agreement. Aside from recurrence, no factors were consistently associated with agreement. Thus, most women were able to accurately report broad categories of treatment but not necessarily specific treatment types. The finding of this study can aid researchers in the use and design of self-administered treatment questionnaires.