The prevalence of attention-deficit/hyperactivity disorder (ADHD) among children in the United States has risen significantly over the past two decades, accompanied by an increase in patients receiving medications (usually stimulants such as methylphenidate) for treatment. This retrospective cohort study found that this surge in diagnoses of ADHD has also been accompanied by an uptick in medication toxicity, as measured by calls to poison control centers. This increase was most prominent between 2000 and 2011, but the rate declined slightly between 2011 and 2014. Most of the calls were classified as unintentional and occurred in patients who had been prescribed a medication for ADHD. However, among adolescents, half of the exposures involved an intentional medication overdose. Although medications for ADHD are generally considered safe—and the vast majority of patients in this study did not require care for their exposure—this study provides an important estimate of the risks associated with these medications and the types of patients who may be most vulnerable.