Anabolic-Androgenic steroids (AAS) are synthetic derivatives of testosterone. While they previously were associated mostly with use among professional athletes, the recent decades have seen a spread of AAS use to the general population. Heightened aggressiveness is one of the most commonly reported side effects of AAS use; however, the reasons behind this association have remained elusive. AAS have recently been shown to lead to neurochemical alterations in brain areas important for the regulation of aggression, as well as frontal areas important for executive functions. The aims of this study were to investigate aggression and levels of executive functioning in long-term AAS users. AAS users with long-term AAS using careers (defined here as 1 year of cumulative use or more) and non-AAS using exercisers were recruited from local gyms and via online forums. The assessment included a semi-structured interview concerning demographic data, exercise habits, self-reports of side effects and pattern of AAS use. Based on this data, estimated lifetime doses of AAS were calculated. Other aspects of pattern of AAS use were age of onset, total duration of use, concomitant drug abuse and AAS dependence. Aggression was assessed using the Buss Perry Aggression Questionnaire (BPAQ), which produces four subscales on different aspects of aggression. Executive functions were assessed using three commonly used neuropsychological tests; the Color Word Interference Test (CWIT), the Trail Making Test (TMT) and the Attentional Network Test (ANT). The results showed a significant and strong main effect of AAS use on several measures of aggression. AAS users with no history of drug abuse displayed significantly higher levels of aggression than controls. Furthermore, estimated lifetime dose, age of onset and duration of use correlated with levels of aggression. Findings on executive functions were somewhat more ambiguous. AAS users performed worse than controls on measures of executive inhibition and executive control. No differences were seen on tests of cognitive flexibility. It is concluded that AAS users display significantly higher levels of aggression compared to non-AAS using individuals, and that these levels are associated with a more severe pattern of AAS use. Furthermore, this investigation provides evidence that AAS users display lower levels of executive inhibition and control, but not flexibility. The implications of this finding for the association between AAS use and aggression are discussed, and suggestions for future research are presented.