The diagnosis of a concurrent infection of Avibacterium paragallinarum and fowl adenovirus (FAdV) in an infectious coryza-like outbreak in the outskirt of Beijing is reported. The primary signs of the infection were acute respiratory signs, a drop in egg production, and the presence of hydropericardium-hepatitis syndrome-like gross lesions. Laboratory examination confirmed the presence of A. paragallinarum by bacterial isolation and a species-specific PCR test. In addition, conventional serotyping identified the isolates as Page serovar A. Fowl adenovirus was isolated from chicken liver specimen and identified by hexon gene amplification. In addition, histopathologic analysis and transmission electron microscopy examination further confirmed the presence of the virus. Both hexon gene sequencing and phylogenetic analysis defined the viral isolate as FAdV-4. The pathogenic role of A. paragallinarum and FAdV was evaluated by experimental infection of specific-pathogen-free chickens. The challenge trial showed that combined A. paragallinarum and FAdV infection resulted in more severe clinical signs than that by FAdV infection alone. The concurrent infection caused 50% mortality compared with 40% mortality by FAdV infection alone and zero mortality by A. paragallinarum infection alone. To our knowledge, this is the first report of A. paragallinarum coinfection with FAdV. The case implies that concurrent infections with these 2 agents do occur and more attention should be given to the potential of multiple agents during disease diagnosis and treatment.