<p>Gastrointestinal nematodes such as <i>Ascaridia galli (A. galli)</i> are prevalent in laying hens kept in production systems with free access to outdoor areas. A pilot study was conducted to establish an infection model with <i>A. galli</i> which then was used in two subsequent experiments to evaluate the impacts of different levels of <i>A. galli</i> infection on performance, egg quality and immune status of laying hens. In an artificial infection study, laying hens were inoculated with low (250), medium (1000), and high (2500) levels of embryonated <i>A. galli</i> eggs/hen. In a natural infection study, hens were ranged on the areas contaminated with <i>A. galli</i> during the artificial infection study. In both studies, uninfected hens served as control groups.</p><p> Infecting hens orally with 500 or 1000 embryonated <i>A. galli</i> eggs in multiple applications was found to be a more reliable method compared to infecting hens using a single dose. The artificial infection study showed that <i>A. galli</i> infection with different dose rates had no effect on feed intake, body weight, and FCR until 40 weeks of age. There was no difference in egg production at 25, 35 and 40 weeks of age. Serum and yolk antibodies against <i>A. galli</i> were higher at 20 weeks post infection.</p><p> Naturally infected hens had a higher infection intensity exhibited by higher intestinal worm counts and excreta egg counts compared to the artificially infected hens. However, this higher infection intensity did not negatively affect egg production, egg mass, feed intake, FCR and egg quality during the experiment. The liver lipid content of the hens with higher <i>A. galli</i> burden were compared to the uninfected hens and the results showed that the infected hens had consistently lower liver lipid reserves compared to the uninfected hens.</p><p> Across the two trials the sensitivity of the ELISA assay was 100% and 96% for serum and egg yolk samples respectively, whereas pooled excreta egg counts had sensitivity of 93%. Measurements of serum and yolk antibody levels can be helpful for the detection of current or prior <i>A. galli</i> infection. The practical and non-invasive method of yolk sample analysis is likely to be as informative as using serum samples to detect <i>A. galli</i> infection. Results of these experiments indicate that <i>A. galli</i> causes no production loss during the first three months of the free range laying hen's production cycle. However, production losses that might occur in the later stages of laying cycle still needs to be investigated.</p>