Breast cancer risk is a common indication for referral to clinical genetics services. UK National Institute of Health and Care Excellence (NICE) guidelines use family history (FH) to stratify by 10-year risk of breast cancer from age 40. Patients are stratified into population risk (PR, 10-year risk <3%), moderate (MR, 3-8%) and high risk (HR, >8%). Women at increased risk are offered screening at or prior to age 40. To assess the clinical effectiveness of current risk stratification, FH data was obtained for all unaffected women with a FH of breast cancer aged <50, referred to cancer genetics from 2000-2010. Patients were risk stratified by NICE criteria, identifying patients who subsequently developed breast cancer. 1,409 women had 15,414 patient-years of follow up. 30 invasive breast cancers developed, 13 in MR and 13 in HR women. Kaplan-Meier analysis demonstrated no significant difference in rate of breast cancer development between PR and MR women from ages 40-49 (Log rank p=0.431). There was a significant difference between ages 40- 49 years between PR and HR women (p=0.036), but not on exclusion of BRCA mutation carriers (p=0.136). NICE absolute 10-year risk thresholds between ages 40-49 were not met in any risk group, when risk was estimated using the guidelines (PR=0.82%, MR=1.68%, HR=3.56%). Our data suggests that improved criteria are required for risk assessment prior to age 50 and screening resources may be best focussed on those with highly penetrant mutations in cancer risk genes.