This literature review summarizes available data on infection with the parasitic roundworm, Ascaridia galli, as a cause of disease in poultry, including the consequences of a conversion to alternative production systems. Ascaridia galli has a direct life cycle with resistant eggs that survive and are easily spread in the environment, especially in systems with bedding materials where the faecal contact is high. The infection is usually subclinical but depending on the infection dose, the symptoms range from weight loss and diarrhea to mortality. Factors such as the feed composition and genetic variation among different hybrids clearly affect the establishment rate of the infection. Ascaridia galli will probably become an increasing problem, with a shift from the traditional battery cages to alternative systems where the risk of re-infection is high.