BACKGROUND To reduce mortality, women with a family history of breast cancer are often screened with mammography before age 50 years. Additional magnetic resonance imaging (MRI) improves sensitivity and is cost-effective for BRCA1/2 mutation carriers. However, for women with a family history without a proven mutation, cost-effectiveness is unclear. METHODS We evaluated data of the largest prospective MRI screening study (MRISC). Between 1999 and 2007, 1597 women (8370 woman-years at risk) aged 25 to 70 years with an estimated cumulative lifetime risk of 15% to 50% for breast cancer were screened with clinical breast examination every 6 months and with annual mammography and MRI. We calculated the cost per detected and treated breast cancer. After incorporating MRISC data into a microsimulation screening analysis model (MISCAN), different schemes were evaluated, and cost per life-year gained (LYG) was estimated in comparison with the Dutch nationwide breast cancer screening program (biennial mammography from age 50 to 75 years). All statistical tests were two-sided. RESULTS Forty-seven breast cancers (9 ductal carcinoma in situ) were detected. Screening with additional MRI costs $123 672 (€93 639) per detected breast cancer. In increasing age-cohorts, costs per detected and treated breast cancer decreased, but, unexpectedly, the percentage of MRI-only detected cancers increased. Screening under the MRISC-scheme from age 35 to 50 years was estimated to reduce breast cancer mortality by 25% at $134 932 (€102 164) per LYG (3.5% discounting) compared with 17% mortality reduction at $54 665 (€41 390) per LYG with mammography only. CONCLUSIONS Screening with MRI may improve survival for women with familial risk for breast cancer but is expensive, especially in the youngest age categories.