Objective: To document inter- and intra-cohort changes in adult ADHD and examine whether changes vary by gender. 

Method: The study analyzed data from the 2007 and 2012 U.S. National Health Interview Survey. 

Results: The prevalence of ADHD among adults aged 18 to 64 years increased from 3.41 percent in 2007 to 4.25 percent in 2012. As expected, patterns of inter- and intra-cohort change varied by gender. At younger ages, inter-cohort gender differences are more distinct due to a spike in prevalence among boys/men born in or after 1980. Consistent with a gender-specific historical period effect, recent intra-cohort increases among women have narrowed the gender gap. 

Conclusion: The gender gap in the prevalence of ADHD among adults decreased by 31.1 percent from 2007 to 2012 due to increased prevalence among adult women of all ages. We discuss these results in relation to diagnostic practice, adult health and well-being, data limitations and needs, and directions for future research.