Nicotine and stimulant medications share similar neurotransmission-related effects in the pre-frontal cortex, but it is unclear if nicotine has a similar benefit on inhibitory control. Impulsivity resulting from deficits in inhibition and sustained attention have been posited as a unifying mechanism of adult ADHD psychopathology. These deficits were quantified in the present study using Go/No-Go task accuracy and intra-individual reaction time variability (RTV). The electro-cortical P3a amplitude indexes inhibitory cognitive processes and sustained attention-related frontal cortex activation in response to infrequent NOGO stimuli. However, little work has characterized the effects of nicotine on P3a or RTV in adult ADHD. Therefore, the effects of the nicotine patch on NOGO P3a amplitude, inhibitory accuracy, and RTV were assessed in non-medicated ADHD adults (12 smokers, 12 never-smokers) in a double-blind, placebo-controlled, repeated-measures design. Nicotine patch, relative to placebo patch, significantly increased NOGO inhibitory accuracy, significantly decreased GO RTV, and significantly increased NOGO P3a peak amplitude at four frontal electrode sites. These results suggest that the nicotine reduces impulsivity in adults with ADHD. The implications of these basic findings to the clinical assessment and treatment of ADHD are discussed. Additional reports at both the basic and clinical levels are needed to confirm and extend these findings.