Objective: The objective of this study was to describe the epidemiology of diagnosed ADHD and the pharmacological treatment of patients with ADHD in Sweden. Specifically, this study estimates the prevalence of patients with a newly registered diagnosis of ADHD over a 5-year period, and the prevalence of all patients with a registered ADHD diagnoses over a 6-year period in Sweden. Method: Two population-based registries were used as data sources for this study; the National Patient Register (NPR) and the Prescribed Drug Register (PDR). The international Classification of Diseases 10th Revison (ICD-10) was used to identify patients with ADHD. Results: The annual prevalence of ADHD in the general population of Sweden was found to be 1.1 per 1,000 persons in the year 2006 increasing to 4.8 per 1,000 persons in 2011. The corresponding prevalence for newly diagnosed patients increased from 0.6 per 1,000 persons in 2007 to 1.3 per 1,000 persons in 2011. The majority of diagnosed patients received pharmacological treatment, with methylphenidate being the most common dispensed drug. Comorbidities in the autism spectrum were most common for younger patients, while substance abuse, anxiety, and personality disorder were the most common comorbidities in older patients. Conclusion: From 2006 to 2011, the number of patients diagnosed with ADHD has increased in Sweden over all ages. The majority of patients diagnosed with ADHD in Sweden received a pharmacological treatment regardless of age. An ADHD diagnosis was often accompanied with psychiatric comorbidity.