Purpose: To assess the frequency of clinical signs in patients with viral acute anterior uveitis (AAU), and their ability to differentiate viral versus non-viral AAU.Methods: 168 patients with AAU, including 84 with presumed viral etiology, were evaluated. Sensitivity, specificity, area under the curve (AUC), positive and negative predictive value were calculated for each clinical sign. The model built with these parameters was tested on a validation group comprising 66 patients with AAU.Results: The most useful clinical signs were unilaterality (sensitivity: 98.8%, specificity: 57.1%), intraocular pressure (IOP) ≥24 mmHg (sensitivity: 68.7%, specificity: 91.7%), and the association between the two (sensitivity: 68.7%, specificity: 95.2%). In the validation group, the model built with these parameters presented AUC of 0.939. Adding iris atrophy AUC increased to 0.97. Considering these signs, it was possible to diagnose viral uveitis in 93.9% of the patients.Conclusion: Unilaterality, IOP≥24 mmHg and iris atrophy are significant predictors of possible viral etiology in AAU.