BACKGROUND: Approximately 110,000 people in the United Kingdom are affected with familial hypercholesterolaemia (FH). At least 75 per cent are undiagnosed. Treatment with statins is effective but effective primary prevention requires early diagnosis. The best strategy to achieve this is unclear. This paper compares the costs and benefits over a 10 year period of two strategies found in our previous modelling: population screening of 16-year-olds or tracing family members of affected patients. METHODS: Computer modelling of time-limited data was conducted. The number available for screening and the potential new cases in England and Wales aged 16-54 years were estimated. The costs (of screening and treatment) and benefits (deaths averted) that might be accrued over 10 years were assessed. RESULTS: Screening 16-year-olds results in 470 new diagnoses, and over 10 subsequent years averts 11.7 deaths at a cost of 6,176,648 pounds sterling, giving a cost per case identified and treated of 13,141 pounds sterling (including a 10 year drug cost of 1,584,918 pounds sterling). By contrast, screening first-degree relatives of known uases results in 13,248 new diagnoses, 560 deaths averted over 10 years, at a cost of 46,430,681 pounds sterling giving a cost per case identified and treated of 3,505 pounds sterling (including 10 year drug cost of 44,645,760 pounds sterling). The cost per death averted would be 3,187 pounds sterling. CONCLUSIONS: Although the two approaches appear similar in cost-effectiveness over a lifetime, the shorter-term (10 year) cost-effectiveness clearly favours family tracing. This represents good value for money compared with common medical interventions, and suggests that pilot FH family tracing programmes should be conducted.