Objective To determine the utility (i.e., positive predictive value [PPV] and time requirement) of an adverse drug event (ADE) trigger tool in Veterans Affairs (VA) nursing homes (NHs); and to describe the most common types of potential ADEs detected with the trigger tool. Design Retrospective chart review. Setting/Patients Veterans residing in three VA NHs between 09/29/2010 and 10/29/2010. Measurement We used the Institute for Healthcare Improvement (IHI)-endorsed NH ADE trigger tool, modified to enhance its clinical relevance to detect potential ADEs. Electronic medical records were screened to identify residents with ≥1 abnormal laboratory value specified in the trigger tool. Main Outcome Measures A potential ADE was defined as the concurrent administration of medication that could cause the abnormal laboratory value. An overall PPV, or proportion of residents with an abnormal laboratory value who had a potential ADE, and average time required to complete each trigger tool assessment were calculated. Results Among 321 Veterans, 50.5% (n=162) had at least one abnormal laboratory value contained in the trigger tool. Ninety-nine potential ADEs involving 146 medications were detected in 65 Veterans. The overall PPV of the ADE trigger tool was 40.1% (65/162), and the average time to complete resident assessments was 8.8 (sd ± 5.7) minutes. The most common potential ADEs were acute kidney injury (n=30 residents), hypokalemia (n=18), hypoglycemia (n=13), and hyperkalemia (n=10). Conclusions The modified NH trigger tool was shown to be an effective and efficient method for detecting potential ADEs.