Abstract Three taita falcon (Falco fasciinucha) nestlings and 3 cohoused hybrid falcon (F rusticolus × F peregrinus) nestlings died after showing lethargy and anorexia for 4–5 days. Major lesions in the falcons were necrotizing hepatitis, splenitis, and lymphoplasmacytic nephritis. One hybrid falcon also had a heterophilic nephritis. Intranuclear inclusion bodies were present in the hepatocytes of the taita falcons and in the renal tubular epithelial cells of 1 hybrid falcon. Adenoviral particles were found in the cloacal content of 2 taita falcons. DNA in situ hybridization revealed aviadenoviral nucleic acid within the nuclei of hepatocytes of a taita falcon and a hybrid falcon and in the tubular epithelial cells of a hybrid falcon. Aviadenoviral DNA was amplified by polymerase chain reaction in the liver of taita falcons and hybrid falcons. The death of these birds was attributed to the aviadenovirus infection; however, the source of the virus was not determined. Predisposing factors for the outbreak o...