A 5-yr retrospective study was conducted to characterize the spectrum of diseases causing mortality in 1301 backyard chickens submitted to the California Animal Health and Food Safety laboratory in Davis, California. Infectious diseases were diagnosed in the majority (60.4%). Viral diseases comprised 50% of the infectious entities, followed by bacterial diseases with an incidence of 39%. Marek's disease in the viral group and Escherichia coli in the bacterial group were the most commonly diagnosed infectious diseases. Zoonotic agents including Aspergillus sp., Salmonella sp., Listeria sp., Mycobacterium sp., Candida sp., and Baylisascaris sp. were detected in 46 (3.5%) birds. Among noninfectious conditions, fatty liver hemorrhagic syndrome and reproductive tract adenocarcinoma were the leading causes of mortality. This analysis provides an overview of backyard chicken diseases for practitioners and avian pathologists working with backyard poultry. In addition, this study illustrates that backyard chickens do not seem to pose a major risk to public health, although zoonoses do comprise a notable portion (5.9% of all infectious cases) of isolated agents.