There is insufficient data regarding the excess direct and indirect costs associated with attention deficit hyperactivity disorder (ADHD). Using the Danish National Patient Registry (2002–2016), we identified 83,613 people of any age with a diagnosis of ADHD or who were using central-acting medication against ADHD (primarily methylphenidate, with at least two prescriptions) and matched them to 334,446 control individuals. Additionally, 18,959 partners of patients aged ≥18 years with ADHD were identified, and compared with 74,032 control partners. Direct costs were based on data from the Danish Ministry of Health. Information about the use and costs of drugs were obtained from the Danish Medicines Agency. The frequencies of visits and hospitalizations, and costs of general practice were derived from data from the National Health Security. Indirect costs were obtained from Coherent Social Statistics. The average annual health care costs for people with ADHD and their partners were, respectively, €2636 and €477 higher than those of the matched controls. A greater percentage of people with ADHD and their partners compared with respective control subjects received social services (sick pay or disability pension). Those with ADHD had a lower income from employment than did controls for equivalent periods up to five years before the first diagnosis of ADHD. The additional direct and indirect annual costs (for those aged ≥18 years) including transfers of ADHD compared with controls were €23,072 for people with ADHD and €7,997 for their partners. ADHD has substantial socioeconomic consequences for individual patients, their partners and society.