Objective: Multiple Endocrine Neoplasia type 1 (MEN1) is associated with an early onset elevated breast cancer risk. This finding potentially has implications for breast cancer screening for females with MEN1. Considering the impact for females with MEN1, regarding distress and anxiety, it is necessary to assess if other risk factors are involved to identify those at greatest risk. Design: A cross-sectional case control study was performed using the Dutch MEN1 cohort, including >90% of the Dutch MEN1 population of 18 years and older. All females with a confirmed MEN1 mutation received a questionnaire regarding breast cancer related endocrine risk factors, cancer family history and other known risk factors for breast cancer. Results: A total of 138 of 165 (84%) eligible females with MEN1 completed the questionnaire. Eleven of the 138 females had breast cancer. Another 34 relatives with breast cancer were identified in the families of the included females, of whom 11 were obligate MEN1 carriers, 14 had no MEN1 mutation and nine had an unknown MEN1 status. The median age at breast cancer diagnosis of females with MEN1 (n=22) was 45 (range 30-80) years in comparison with 57.5 (range 40-85) years in female relatives without MEN1 (n= 14) (p=0.03) and 61.2 years in the Dutch reference population. Known endocrine risk factors as age at menarche, oral contraception use, pregnancy, age at first birth, parity and breast-feeding were not different for females with and without breast cancer. In addition, smoking and alcohol consumption did not differ between respondents with and without breast cancer. Conclusion: The increased breast cancer risk in MEN1 carriers was not related to other known breast cancer risk factors or familial cancer history and therefore breast cancer surveillance from the age of 40 years for all females with the MEN1 is justifiable.