OBJECTIVES: For models that simulate patients over a long span, such as from birth to life expectancy, the baseline HRQoL can be incorporated. Typically this means that younger people have a higher utility than older people. The aim of this study was to investigate the impact of including age-specific baseline utilities in a model that simulated women at elevated risk of developing breast cancer from ages 20 to 85. METHODS: A model was developed to evaluate the impact on costs and benefits of breast cancer surveillance in a population of women with a BRCA1 mutation. Women were modelled from age 20 to 85. QALY reductions were associated with the treatment of cancer and were stage-specific. The model was evaluated incorporating age-specific baseline QALYs and also where all ages had a baseline QALY of 1. The impact of age-specific baseline QALY inclusion was evaluated in terms of the ICERs for different surveillance strategies. RESULTS: The incremental cost of each intervention and the interventions included in the cost-effectiveness efficiency frontier were unaffected by the choice of baseline HRQoL. However, both the average and incremental cost-effectiveness ratios were changed. For interventions on the cost-effectiveness efficiency frontier, all ICERs were less than €100,000/QALY when age-specific baseline HRQoL values were used. ICERs reduced by an average €11,520 when a uniform baseline HRQoL was used. CONCLUSIONS: The use of age-specific baseline HRQoL in a cost-effectiveness model needs to be carefully considered. Inclusion of age-specific baseline HRQoL can favour interventions with an impact at a younger age. Whether age-specific or uniform baseline data are used in a model, the alternative should be considered in a sensitivity analysis.