Psychologists have standardized competency-to-stand-trial (CST) assessments through the development of specialized CST measures. However, their research has largely neglected the possibility that CST measures may be stymied by feigning mental disorders and concomitant impairment. The current study is the first systematic examination of (a) how feigned mental disorders may affect CST measures and (b) which scales are effective at identifying feigned cases. Bona fide patients (n = 65) were compared with suspected malingerers (n = 22) on 3 CST measures: the Georgia Court Competency Test (GCCT), the MacArthur Competence Assessment Tool--Criminal Adjudication, and the Evaluation of Competency to Stand Trial--Revised (ECST-R). Results indicated that these CST measures are vulnerable to feigning. The development of specialized GCCT and ECST-R scales yielded moderately effective screens for feigned mental disorders in the context of CST evaluations.