The objective of this study was to explore the factors that influence perceived personal risk of developing breast cancer (BC) in younger women (<35) who are considering or have undergone bilateral prophylactic mastectomy (BPM). Qualitative interviews guided by interpretative phenomenological analysis were conducted with 46 women who had a strong family history of BC and had either undergone (n = 26) or were considering (n = 20) BPM. Participants were recruited from Australia and New Zealand via hospitals, a genetics clinic, a research cohort, a registry and online. Three main themes were identified: information that increases fear of BC and death, underlying anxiety and fear and screening anxiety. A further two themes: relief following surgery and confusion about residual risk following surgery were identified. Younger women (<35) appeared to have heightened and sometimes inaccurate perceptions of their BC risk. They appeared less relieved of anxiety and fear of developing BC by BPM surgery, in comparison to previous research with older women (>40). Those who had undergone BPM seemed more anxious about their risk of developing BC than those who were still considering surgery. This research has important implications for practice, particularly improving communication of accurate risk statistics. Future research should examine why some women interpret information differently and explore the benefits of psychological consultation for very anxious women.