Background: Familial hypercholesterolemia (FH) is a genetic disorder estimated to affect 0,4 % of the world's population (1 in 250). Patients with FH have abnormally high LDL-cholesterol.  Aim: The aim of this study was to estimate the prevalence of FH in Stockholm County and to evaluate the health economic impact of diagnosing people with FH early in life. Methods: Two algorithms were used to estimate the number of people with high LDLcholesterol. The first method applied data on cholesterol measurements from patients in Stockholm County between 2006-2008 and a modified version of Dutch Lipid Clinic Network. The second method was based on dispensed prescriptions of ezetimibe, lomitapide, evolucumab and alirocumab during 2019. A health economic model was created to estimate the economical outcome of diagnosing and treating patients early before undergoing a cardiovascular event. Results: The prevalence of FH in Stockholm County was estimated to 0.63 %, corresponding to a total of 12 000 individuals. The accumulated costs over 20 years for FH is estimated to be more than 1,1 billion SEK for diagnosed and treated patients, and 1,7 billion SEK for undiagnosed and untreated patients. Conclusions: The prevalence of FH in Stockholm County is probably higher than previously suggested. Early diagnosis and treatment is an investment for society and necessary for the patients to prevent cardiovascular events and improve quality of life.