Only recently have studies included a female Attention Deficit Hyperactivity Disorder (ADHD) sample when investigating neurocognitive functioning of individuals with ADHD. As such, the generalizability of findings of impaired executive functioning is limited to ADHD males. This study compared four groups: 30 male controls, 35 female controls, 24 males with ADHD, and 25 females with ADHD, aged 13 to 17 years. Participants were assessed using the K-SADS-PL and Conners' Rating Scales and completed tests of rapid naming, processing speed, memory, inhibition, set-shifting, and interference. Results showed that the males with ADHD and females with ADHD performed similarly with only one notable difference: males with ADHD showed some evidence of more impaired inhibition than females with ADHD. In contrast, after controlling for reading ability, comorbidity, and IQ, both males and females with ADHD showed some impairment in working memory, naming speeds, processing abilities, and inhibitory deficits as compared to controls. This study supports the growing literature documenting impaired neurocognitive functioning in both males and females with ADHD. (American Psychiatric Association, 2000).Given the insurmountable evidence showing deficits in cognitive and executive functioning (Tannock, 1998), behavioural inhibition (Barkley, 1997Schulz et al., 2004;Slaats-Willemse, Swaab-Barneveld, De Sonneville, Van Der Meulen, & Buitelaar, 2003), motor control (Carte, Nigg, & Hinshaw, 1996), processing and naming speed (Tannock, Martinussen, & Fritjers, 2000), working memory (Martinussen, Hayden, Hogg-Johnson, & Tannock, 2005;West, Houghton, Douglas, & Whiting, 2002), and estimation of time (Toplak, Rucklidge, Hetherington, John, & Tannock, 2003) in mainly male ADHD samples, there has been a recent focus to determine whether these well documented problems in males with ADHD extend to females with ADHD.While earlier studies suggested that females with ADHD may be less impaired than males with ADHD in tests of cognitive functioning (Seidman et al., 1997), evidence has been building that females are likely as impaired as males with ADHD, and in some cases, more impaired. Consistent with an earlier meta-analytic review (Gaub & Carlson, 1997), a recent meta-analysis concluded that while ADHD females show poorer intellectual functioning than ADHD males (Gershon, 2002), no other differences in cognitive functioning were noted.Arcia and Conners (1998) did not find any gender differences in ADHD on tests of inhibition, spatial memory and planning, and overall cognitive abilities. While Rucklidge and Tannock (2002) failed to document any gender differences in an ADHD sample on tests of naming speed, working memory, and inhibition they found males with ADHD were slower with processing information than females with ADHD. A recent study by Seidman and colleagues (2005) found that across two developmental age groups (preteen and teenage years), their sample of ADHD girls and boys diagnosed using DSM-III-R showed similar levels of executive dysf...