The major objective of the study was to examine the effects of nicotine on ADHD symptoms, moods, and cardiovascular activity. The study investigated the effects of nicotine patches on behavioral regulation in adult smokers and nonsmokers with ADHD. Smokers and nonsmokers with ADHD participated in two conditions: (1) nicotine patch and (2) placebo patch. During each condition, symptoms, moods, and side effects were assessed for 2 days during waking hours. An electronic handheld diary, programmed to prompt the participant twice per hour, recorded ADHD symptoms (e.g., difficulty concentrating, impulsivity, etc.), negative moods (e.g., anger, stress), and nicotine side effects (nausea, dizziness). Heart rate and blood pressure were recorded with lightweight ambulatory monitors to indicate cardiovascular activity. Results provided information about the effects of nicotine patches on behavioral regulation in adult smokers and nonsmokers with ADHD.