The goal of this investigation was the development of an inconsistency scale (ICN-SF) for the personality assessment inventory-short form (PAI-SF). In Study 1, 503 inpatient profiles were randomly assigned to a derivation or cross-validation sample. Ten correlated item pairs were identified using the derivation sample and placed on the ICN-SF. Psychometric properties of the ICN-SF total scores were comparable in the derivation and cross-validation samples. Total ICN-SF scores in both samples were significantly lower than scores obtained from computer-generated random samples. Diagnostic efficiency statistics are reported using multiple cut-off scores at various base rate estimates. ICN-SF scores greater than 8 reasonably balanced sensitivity and specificity rates. This cutoff correctly classified 92% of the random protocols and inaccurately classified 9% of the patient protocols in study 1. In study 2, PAI-SF scores from 627 forensic and civil inpatients produced similar results, effectively identifying cases with elevated scores on the full-form inconsistency scale. Overall the results of both studies suggest that the ICN-SF can aid examiners in assessing for inconsistent responding.