The aim of this study was to describe the prevalence and incidence of ADHD medication prescribing, by age and gender, from 2005 to 2015 in Canadian primary care. A population-based retrospective cohort study was conducted to evaluate the prescribing of ADHD medications between 2005 and 2015 using electronic medical record data. Yearly prevalence and incidence of ADHD medication prescribing were calculated for preschoolers (up to 5 years old), school-aged children (6-17 years old), and adults (18-65 years old) along with a description of the types of ADHD medications prescribed between 2005 and 2015. Between 2005 and 2015, there was a 2.6-fold increase in the prevalence of ADHD medication prescribing to preschoolers, a 2.5-fold increase in school-aged children, and a fourfold increase in adults. There was a corresponding rise in incidence of prescribing although this rise was moderate and estimates were much lower compared with prevalence. The most commonly prescribed medication was Methylphenidate (65.0% of all ADHD medications prescribed). Although the prevalence of ADHD has remained stable over time, this study found an increase in the prescribing of ADHD medications in all age groups between 2005 and 2015. Incidence of new prescriptions was small relative to prevalence, suggesting that longer term treatments are being adopted.