Background Many individuals with hepatitis C virus (HCV) infection are undiagnosed. Purpose This study describes the development and the use and outcomes of a mass media campaign, combined with an Internet risk assessment and an Internet-mediated blood-testing procedure for HCV to identify individuals infected with HCV in the general population. Methods From April 2007 to December 2008, individuals in HCV risk groups were referred to an online, previously validated risk-assessment questionnaire at www.heptest.nl . Individuals at risk could download a referral letter for a free, anonymous HCV blood test in a nonclinical setting. Test results could be obtained online, 1 week later, using a personal log-in code. Anti-HCV-positive participants were requested to visit the Public Health Service for confirmation and RNA testing. Chronically HCV-infected individuals were referred for treatment. Data were analyzed in 2009–2010. Results The website attracted 40,902 visitors. Of the 9653 who completed the questionnaire, 2553 were at risk for HCV (26.4%). Main reported risk factors were a blood transfusion prior to 1992 and noninjecting drug use. Of the 1480 eligible for the blood test, 420 opted for testing (28%). HCV antibodies were detected in 3.6% ( n =15, 95% CI=2.1%, 5.7%); of the 12 with a chronic HCV infection, six began treatment. Conclusions Internet-mediated risk-based testing for HCV has proved to be a feasible and effective strategy to identify undiagnosed HCV infection in the general population. All HCV-infected individuals belonged to hard-to-reach populations. Test uptake was 28%, which is high for an online project that includes blood testing. Because Internet-mediated testing is low-cost, this strategy holds promise for future screening.