Two wild adult Common Loons (Gavia immer) were evaluated after being found stranded in mainland north-central Florida on separate occasions. On the basis of upper airway endoscopic and cytologic findings, we diagnosed severe ulcerative tracheitis ante-mortem in one of the birds while more subtle lesions were observed in the other. A novel herpesvirus was detected in antemortem tracheal samples using nested consensus PCR amplification of the polymerase gene and sequencing. Despite prolonged intensive medical care, the bird with severe lesions failed to improve and was euthanized 9 days after endoscopy. No viral inclusions were evident histologically in the lesions. However, an undulating tracheal mucosa in a ‘‘mountain ridge’’ pattern, resulting from epithelial regeneration and hyperplasia, was present, as is seen in the late stages of infectious laryngotracheitis in chickens. The second bird recovered and was released. The genetic distance between this and other characterized herpesviruses supports placement of this virus as a novel species, referred to as Gaviid herpesvirus 1 (GavHV1). Phylogenetically, GavHV1 clusters within the genus Iltovirus. The relationship between the observed lesions and the virus remains to be demonstrated.