Attention Deficit Hyperactivity Disorder (ADHD) has been medicalized in the United States since the 1960s. Primarily used in North America until the 1990s, ADHD diagnosis and treatment have increasingly been applied internationally. After documenting the expansion of ADHD in a global context, this paper presents five brief international examples examining ADHD usage and expansion: the United Kingdom, Germany, France, Italy and Brazil. We then identify and describe several vehicles that facilitate the migration of the ADHD diagnosis: the transnational pharmaceutical industry; the influence of western psychiatry; moving from ICD to DSM diagnostic criteria; the role of the Internet including the related advent of easily accessible online screening checklists; and advocacy groups. Finally, we discuss what this globalization of a diagnosis reflects about the potential global medicalization of other conditions.