OBJECTIVES: To compare socio-demographic characteristics, comorbidities, health care resource use and work productivity assessments among adults diagnosed with attention-deficit/hyperactivity disorder (ADHD) from Europe (E) and the United States (US).  METHODS:  Data are from the 2011 National Health and Wellness Survey (NHWS), conducted online annually by Kantar Health among samples of adults obtained from international consumer panels. Data reported in this study were gathered September-December 2011 in Germany, UK, France, Spain, Italy, and the U.S. Comparisons of ADHD and non-ADHD control populations were presented previously. Those results are extended below, by comparing to differences between European and U.S. study participants, using chi-square tests of proportions. RESULTS:  A total of 235 European and 676 US NHWS participants reported having received a diagnosis for ADHD from a health care professional.  Diagnosed ADHD respondents were more frequently male (59% E vs. 56% US) and less likely married (38% E vs. 33% US) than non-ADHD controls. ADHD respondents were more likely to report sleep difficulties (67% E vs. 44% US; p<.05), anxiety (61% E vs. 58% US), depression (59% E vs. 60% US), or headaches (57% E vs. 63% US) than non-ADHD controls. Likelihoods of an emergency room visit (34% E vs. 24% US; p<0.05), or a hospitalization (32% E vs. 12% US; p<0.05) within the past 6 months were greater among diagnosed ADHD respondents than non-ADHD controls.  Diagnosed ADHD respondents were also more likely to report health-related work productivity loss (55% E vs. 34% US; p<0.05). CONCLUSIONS: Adults from Europe and the US reported high rates of comorbidity with various mental, emotional, or physical disorders, high rates of health resource utilization, and high rates of health-related work productivity loss, with many of these higher among European than US participants.