This study was designed to (1) evaluate the effect of narratives used in a popular, publicly available patient decision aid for early-stage breast cancer on hypothetical treatment decisions and attitudes toward the decision aid and (2) explore the moderating effects of participant numeracy, electronic health literacy and decision-making style. Two hundred women were asked to imagine that they had been diagnosed with early-stage breast cancer and viewed one of two versions of a video decision aid for early-stage breast cancer. The narrative version of the aid included stories from breast cancer survivors; the control version had no patient stories. After viewing the video decision aid, participants made a hypothetical treatment choice between lumpectomy with radiation and mastectomy, answered several questions about their decision, and evaluated the quality of the decision aid. Participants received $100 for completing the study. The two conditions differed in their motivations for the treatment decision and perceptions of the aid's trustworthiness and emotionality but showed no differences in preferences for surgical treatments or evaluations of the decision aid's quality. However, the impact of patient narratives was moderated by numeracy and electronic health literacy. Higher levels of numeracy were associated with decreased decisional confidence and lower ratings of trustworthiness for the decision aid in the narrative video condition but not in the control video condition. In contrast, higher levels of electronic health literacy were associated with increased decisional confidence and greater perceptions of trustworthiness and credibility of the decision aid in the narrative video condition but not the control video condition.