BACKGROUND: Clinical decision support alerts for laboratory testing have poor compliance. Once-per-visit alerts, triggered by reorder of a test within the same admission, are highly specific for unnecessary orders and provide a means to study alert compliance. METHODS: Once-per-visit alerts for 18 laboratory orderables were analyzed over a 60-month period from September 2012 to October 2016 at a 1200-bed academic medical center. To determine correlates of alert compliance, we compared alerts by test and provider characteristics. RESULTS: Overall alert compliance was 54.5%. In multivariate regression, compliance correlated with length of stay at time of alert, provider type, previous alerts in a patient visit, test ordered, total alerts experienced by ordering provider, and previous order status. CONCLUSIONS: A diverse set of provider and test characteristics influences compliance with once-per-visit laboratory alerts. Future alerts should incorporate these characteristics into alert design to minimize alert overrides.