Objective: The literature on Attention Deficit Hyperactivity Disorder (ADHD) provides compelling evidence for sleep dysfunction in these individuals, including irregularities on polysomnography and subjective complaints of poor sleep efficiency. Sleep dysfunction in ADHD has been associated with increases in self and informant-reported behavioral symptoms of inattention, hyperactivity, and impulsivity. Few studies have evaluated the relation between sleep dysfunction and neuropsychological variables of executive functions in adults with ADHD. Method: Seventeen subjects with ADHD, six with a prior ADHD diagnosis and eleven diagnosed with probable ADHD based on their neuropsychological profile (% male = 70.6, mean age = 27.8, SD = 9.5) were administered the Wechsler Adult Intelligence Scale, 4th Edition (WAIS-IV), Trail-Making Test B, Ruff 2 & 7 Selective Attention Test, and the Pittsburgh Sleep Quality Index (PSQI). Results: A bivariate correlation analysis revealed strong negative correlations between sleep dysfunction (PSQI Total Score) and composite scores of the WAIS-IV Processing Speed Index (PSI) (r = −.69, p < .01) and WAIS-IV Working Memory Index (WMI) (r = −.51, p = .04), as well as moderate negative correlations between PSQI Total Score and both Trail-Making Test B (r = −.50, p = .04) and Ruff 2 & 7 Total Speed (r = −.48, p = .05) T- scores. Conclusion(s): Sleep dysfunction is associated with poorer performance on measures of executive functioning in adults with ADHD. Clinicians should routinely assess for sleep dysfunction in the neuropsychological evaluation of ADHD.