Psychological assessments of Attention Deficit/Hyperactivity Disorder (ADHD) must consider possible feigning of ADHD symptoms and simulated deficits on attentional measures. Studies have consistently found that motivated examinees can easily feign ADHD with little research focused on its detection. Via a between-subjects simulation design, the current study investigated the MMPI-2-RF and the Conners Infrequency Index (CII) in a university sample by comparing four groups: feigned ADHD, feigned mental disorders, genuine ADHD, and non-ADHD controls. Encouragingly, the CII evidenced moderate discriminability between feigned ADHD and (a) genuine ADHD (d = 0.97) as well as (b) feigned mental disorders (d = 0.96). Because the MMPI-2-RF F-family scores did not differentiate ADHD feigners from other feigners or genuine ADHD, a Dissimulation (Ds) ADHD (Ds-ADHD) scale was developed by utilizing erroneous stereotypes as the detection strategy. While requiring cross-validation, the initial data demonstrated good discriminant validity in distinguishing feigned ADHD from both genuine ADHD and general feigning. As noted in the Discussion, ADHD assessments must systematically take into account examinees’ level of effort and actively evaluate the possibility of feigned ADHD.