Psychological assessments of competency-to-stand-trial (CST) referrals must consider whether the defendants' impairment is genuine or feigned. This study addressed feigning on the Evaluation of Competency to Stand Trial--Revised (ECST-R), a standardized interview designed for assessing dimensions of CST and screening for feigned CST. In particular, this study examined the effectiveness of the ECST-R's Atypical Presentation (ATP) scales as screens for feigned incompetency. It examined ATP scales for (a) jail detainees (n=96) in simulation and control conditions and (b) inpatient competency cases (n=56) in clinical comparison and probable malingering groups. Comparisons of ATP scales yielded very large effect sizes for feigners when compared with jail controls (mean d=2.50) and genuine inpatient competency cases (mean d=1.83). Several cut scores were established with very few false negatives and robust sensitivity estimates. In summary, the ECST-R ATP scales appear to be homogenous scales with established clinical use as feigning screens in CST evaluations.