INTRODUCTION: Previous research has identified gaps in cancer survivors' knowledge of their diagnosis and treatment. This study assessed the effect of treatment summaries on survivors' accuracy in reporting details of diagnosis and treatment. METHODS: Written surveys were completed by 203 breast cancer survivors and 141 colorectal cancer survivors diagnosed between 1999 and 2008 at a cancer center in the Minneapolis, MN, area (78 % response rate). All completed the survey before and again 17 months after receiving a treatment summary, which was sent to them upon request. Accuracy of response at each assessment was compared to cancer registry and medical records. RESULTS: Both breast and colorectal cancer survivors showed significant improvement in accuracy on stage of disease, and breast cancer survivors showed significant improvement in accuracy on morphology, estrogen receptor status, progesterone receptor status, receipt of hormone therapy, and receipt of doxorubicin after receiving the treatment summary. Breast cancer survivors and older individuals were more likely than colorectal cancer survivors or younger individuals to indicate that they used the treatment summary in completing the second survey. Even for items on which accuracy improved significantly, however, patient knowledge remained incomplete. CONCLUSIONS: The provision of treatment summaries can improve cancer survivors' knowledge of details about their diagnosis and treatment. IMPLICATIONS FOR CANCER SURVIVORS: Treatment summaries can meet the specific goal of increasing patient knowledge. Their effectiveness might be greater if presented during a dedicated survivorship health care appointment.