Problem: According to emerging research, adult Attention-Deficit/Hyperactivity Disorder (ADHD) is an often misunderstood psychiatric diagnosis that can be easily overlooked in the clinical setting. A systematic review of the literature revealed that improper treatment may include decreased knowledge of diagnosis, fear of treating adults with stimulant medications, or disbelief that ADHD persists into adulthood. Purpose and Scope: The purpose of this Evidence-Based Practice (EBP) project was to describe the level of nurse practitioner (NP) knowledge regarding adult ADHD before and after NP participation in a teaching intervention addressing adult ADHD. Using descriptive-interventional methodology, the study variable of NP knowledge regarding adult ADHD was tested using a tool developed by Rostain, Power, and Atkins and adapted for the purposes of this interventional design. The adapted instrumentation, the Nurse Practitioner Adult Attention-Deficit/Hyperactivity Disorder Knowledge Survey (NPAAKS), included a 20-item 3-point Likert-scale questionnaire regarding assessment, diagnosis, and treatment of adult ADHD. Goal and Objectives: The goal of the project was to successfully implement an online teaching intervention for NPs regarding primary care assessment, diagnosis, and treaatment of adult ADHD. The objectives were to: (a) describe aggregate demographic characteristics of the NP participants, (b) describe pre-intervention NP knowledge regarding adult ADHD, (c) describe post-intervention NP knowledge regarding adult ADHD, and (d) describe the level of NP knowledge regarding adult ADHD before and after NP participation in a teaching intervention addressing adult ADHD. Plan and Evaluation: Phase One: Conduct a literary needs assessment using a published evidence-based critique template. Phase Two: Design an online teaching intervention using the EBP approach. Phase Three: Implement an online teaching intervention for a projected sample of NP participants through a national online listserve. Phase Four: Evaluate the level of NP knowledge regarding adult ADHD before and after NP participation in a teaching intervention addressing adult ADHD. Outcomes and Results: Pre-intervention and post-intervention measures revealed a significant increase in level of NP knowledge regarding adult ADHD following NP participation in the online teaching intervention addressing adult ADHD. Self-reported NP knowledge regarding adults ADHD increased from a mean score of 3.98 at pre-test to a mean score of 7.42 at post-test. Moreover, participant total score performance on the NPAAKS increased from a mean score of 24.02 at pre-test to a mean score of 56.72 at post-test, while reliably estimates based on internal consistency for the instrumentation also achieved stability with regard to the tool’s performance in this interventional design.