Objective Psychiatric patients sometimes show poor performance or exaggerated symptoms as malingering for secondary gain. The aim of this study was to introduce cut-off scores for detecting poor performance using Wechsler Adult Intelligence Scale (WAIS) in psychiatric patients.Methods Participants were 261 in- and out-patients who visited psychiatry department. They were classified into 4 group- 1) military service, 2) traumatic brain injury (TBI), 3) psychosis, 4) neurosis. A Digit Span subtest (called as Reliable Digit Span, RDS) of WAIS was used to detect malingering. This study considered a score of 10% base rate as RDS cut-off score.Results The RDS cut-off score was shown at 7 pts for military service group, at 3 pts for TBI group, at 6 pts for psychosis group, and at 6 pts for neurosis group.Conclusion This study first introduced RDS cut-off scores for malingering psychiatric patients in South Korea. In clinical practice, clinicians may be able to utilize the RDS cut-off scores for malingering-suspected patients. In particular, for patients with military service issues, 7 or less pts of RDS can be used for detecting and inferring their malingering.