The utility of the Structured Interview of Reported Symptoms [SIRS; Rogers, R., Bagby, R. M., & Dickens, S. E. (1992). Structured Interview of Reported Symptoms professional manual. Odessa, FL: Psychological Assessment Resources], Improbable Failure Rate (IF) scale in pretrial (N = 64) and clinical (N = 153) samples was explored. Internal consistencies of the IF items were α =.81 and α =.92, respectively, with split-half reliabilities of .89 and .84, respectively. The IF scale loaded distinctly from the SIRS primary (psychosis) scales in principal components analysis, and the pattern of performances among clinical groups were as expected (e.g., normal controls outperformed patients with focal lesions and dementia, CHI patients outperformed dementia patients). Performance on the IF items was correlated with MMSE score (r =−.59, p >.001), age (r =.53, p ≤.001), and education (r =.31, p ≤.001), but not with Barona estimated FSIQ (r =−.14, p=.08). For normals and psychiatric patients there was a clear falling off of IF error scores after 1 error, and for CHI patients the fall off began after 2 errors. Results lend credence to the SIRS IF scale as an acceptable screening measure for feigned cognitive abilities.