Increased mortality was reported in two flocks of Muscovy ducklings from two consecutive hatches originating from the same breeder flock. Coughing, dyspnea, and gasping were observed in some ducklings between 6 and 11 days of age. Opaque white plugs of exudate were seen in the tracheas with some ducklings having multiple tracheal plugs. Tracheal and bronchial epithelium was hyperplastic and superficial epithelial cells contained eosinophilic intranuclear viral inclusions. Virus particles compatible with adenovirus morphology were observed in tracheal epithelial cells by electron microscopy and in the supernatant from cell cultures inoculated with filtered tracheal homogenates. The isolated virus was genetically indistinguishable from duck adenovirus 1 (DAdV-1). Our report confirms for the first time the presence of DAdV-1 in Canada and also reports for the first time adenovirus-associated respiratory disease in ducklings and supports previous findings that some DAdV-1 can be pathogenic even in waterfowl.