Duck circovirus (DuCV) is a viral disease of ducks caused by a small DNA virus from the family Circoviridae. The infection is often subclinical, but the virus has a significant immunosuppressive effect—it primarily damages the bursa of Fabricius, the spleen, and other immune organs, thereby increasing the ducks’ susceptibility to other infections. Young ducks are particularly susceptible; they may exhibit stunted growth, weight loss, poor plumage, diarrhea, increased morbidity, and higher mortality rates. DuCV itself often does not cause pronounced clinical signs, but it significantly contributes to the development of mixed infections, which can lead to economic losses on farms. PCR testing is most commonly used for diagnosis, as it allows for sensitive and reliable detection of viral DNA. There is currently no specific treatment or commercially available vaccine against DuCV; therefore, prevention relies on good hygiene, biosecurity measures, limiting the introduction of infection, and maintaining good animal husbandry conditions. Timely laboratory diagnosis is particularly important for determining the causes of increased morbidity, deteriorated production performance, or recurrent secondary infections on a farm.