BRCA1/2 mutation carriers are recommended to undergo risk-reducing salpingo-oophorectomy (RRSO) at 35-45 years of age. While substantially decreasing ovarian cancer risk, this induces immediate menopause. The aim of the Harmony study is to assess long-term health effects of premenopausal RRSO in women with high familial risk of breast and/or ovarian cancer on cardiovascular disease, bone health, cognitive functioning, urological complaints, sexual functioning and quality of life. We will conduct a multicenter, cross-sectional study with prospective follow-up, nested in a nationwide cohort of women at familial risk of breast and/or ovarian cancer. Five-hundred women who underwent RRSO before 45 years of age, with ≥10 years of follow-up after RRSO, will be compared with 250 women (frequency-matched on current age) who did not undergo RRSO before the age of 55 and therefore went through menopause naturally. Participants will complete an online questionnaire, a cardiovascular assessment and assessment of bone mineral density. Cognitive functioning will be assessed objectively with an online neuropsychological test battery. This study will improve the future counselling of women about the long-term health effects of premenopausal RRSO.