BACKGROUND: Despite its importance, little is known about internal medicine (IM) residents' ability to assess and communicate a patient's overnight risk during the resident-to-resident handoff. OBJECTIVE: To evaluate IM residents' ability to identify patients at risk for clinical deterioration using the Patient Acuity Rating (PAR) tool (scored on a 1-7 symmetric scale; 1="Extremely unlikely", 7="Extremely likely"), and to measure how well IM residents conveyed a patient's potential for clinical deterioration during day-to-night handoff. DESIGN AND PARTICIPANTS: Observational cohort study of 46 postgraduate year 1 (PGY-1) and 32 postgraduate year 3 (PGY-3) internal medicine residents rotating on one of four general medicine services from October 2013 through January 2014. MAIN MEASURES: Primary outcomes were (1) level of agreement between resident handoff giver and receiver regarding patients' clinical risk and (2) accuracy of resident-assigned PAR score in predicting a patient's risk of clinical deterioration over the subsequent 24 hours. KEY RESULTS: Analysis of PGY-1 giver-receiver handoff agreement revealed an intraclass correlation coefficient (ICC) (95 % CI) of 0.51 (0.45-0.56), while PGY-3 giverreceiver agreement yielded an ICC (95 % CI) of 0.42 (0.36-0.47). Based on 865 ratings of 378 patients, PGY-1 handoff giver PAR scores of 5 and 6+ were significantly associated with increased odds of clinical deterioration within 24 hours (aOR=6.5 and 12.4; P=0.03 and 0.005, respectively). For the 1,170 PAR ratings of 438 patients assigned by PGY-3 handoff givers, PAR scores of 4, 5, and 6+ were significantly associated with increased odds of an event within 24 hours (aORs=6.0, 9.6, and 18.1; P=0.03, 0.01, and 0.0008, respectively). CONCLUSIONS: The PAR is a useful tool to quantify IM residents' judgment of patient stability, and may be particularly valuable during resident handoff, given that the level of agreement between giver and receiver regarding patient risk is only fair.