Background: Subclinical depressive symptoms are highly prevalent among adolescents and are associated with negative consequences, which may pose an economic burden for society. We conducted a prevalence-based cost-of-illness study using a societal perspective to investigate the cost-of-illness of subclinical depressive symptoms among adolescents. Methods: Using a bottom-up approach, cost questionnaires were assessed to measure costs from 237 Dutch families with an adolescent aged 11–18 with subclinical depressive symptoms (of which 34 met the criteria of a depressive disorder). The study is registered in the Dutch Trial Register (Trial NL5584/NTR6176; www.trialregister.nl/trial/5584). Results: Our calculations show that adolescents with subclinical depressive symptoms cost the Dutch society more than €42 million annually, expressed in costs related to depressive symptoms. Secondary analyses were performed to test the reliability and stability of the costs. When costs related to psychological problems were considered, the annual costs amounted to €67 million. The total societal costs related to physical problems amounted to approximately €126 million. All costs combined (depressive, psychological, behavioural and physical problems and other reasons) amounted to a €243 million. Total costs were highest for physical-related problems of the adolescent (52% of the total costs), followed by psychological (28%), depressive (17%) and behavioural problems (1%). Using an international prevalence rate, societal costs related to depressive symptoms resulted in €54 million a year. Conclusions: Cost-effective prevention programmes seem warranted given the high societal costs and risk of future costs as subclinical depressive symptoms could be a precursor of clinical depression later in life.