Recent evidence has investigated the cost-effectiveness of magnetic resonance imaging (MRI) in younger women with a BRCA1 mutation. However, this evidence has not been contrasted with existing cost-effectiveness standards to determine whether screening is appropriate, given limited societal resources. We constructed a Markov model investigating surveillance tools (mammography, MRI, both in parallel) under a National Health Service (NHS) perspective. The key benefit of MRI is that increased sensitivity leads to early detection, and improved prognosis. For a 30- to 39-year-old cohort, the cost per quality-adjusted life year (QALY) of mammography relative to no screening was 5,200 pounds. The addition of MRI to this costs 13,486 pounds per QALY. For a 40- to 49-year-old cohort, the corresponding values were 2,913 pounds and 7,781 pounds. Probabilistic sensitivity analysis supported the cost-effectiveness of the parallel approach of mammography and MRI. It is necessary to extend this analysis beyond BRCA1 carriers within this age group, and also to other age groups.