The present studies focus on strategies for detecting back irrelevant responding (BIR) on the Personality Assessment Inventory (PAI; L. C. Morey, 1991). Moderate BIR levels can greatly affect the clinical scales of the PAI. Further, the PAI's Inconsistency and Infrequency validity scales are less than optimal for detecting BIR. L. C. Morey and C. J. Hopwood (2004) developed an alternative strategy for detecting BIR that involves comparison of 2 scales from the PAI short-form with the same 2 scales from the PAI full-instrument. The present study examines how different BIR levels affect the clinical, treatment, and interpersonal scales of the PAI in 2 psychiatric inpatient samples. The effectiveness of various strategies for detecting BIR in an inpatient setting is also discussed. Consistent with previous research, moderate rates of BIR impacted several PAI scales in a meaningful way. The Inconsistency and Infrequency validity scales of the PAI were relatively ineffective for detecting low-to-moderate BIR levels. Conversely, the short-form full-instrument comparison strategy was much more sensitive to BIR. Finally, a new BIR detection indicator is presented that improves sensitivity rates for detecting all BIR levels in an acute setting. The implications of these results for detecting BIR in inpatient settings are discussed.