Background: Over the last decade, an increasing body of research has indicated that celiac disease and non-celiac gluten sensitivity (NCGS) is related to various aspects of psychological as well as gastrointestinal functioning. People with Down syndrome struggle with impaired psychological functioning and increased prevalence of gluten-related disorders. Nygaard et al. (2001) found anti-gliadin IgA and IgG, two possible indicators of NCGS, to be related to cognitive/motor functioning in children with Down syndrome. However, more research is needed on how NCGS affects psychological functioning. Method: We assessed cognitive/motor functioning of 21 children with Down syndrome and their prevalence of anti-gliadin IgA and IgG. Parents assessed parenting stress and their child’s gastrointestinal symptoms, behavioral/emotional problems, health-related quality of life, and curiosity through questionnaires. The relationship between NCGS and facets of psychological functioning were investigated using non-parametric and parametric correlational methods, and linear models. Path analysis was used to investigate whether the relationship between NCGS and cognitive/motor functioning was mediated by curiosity. Results: No significant relationship were found between NCGS and psychological functioning. Effect sizes indicated that anti-gliadin IgA and IgG are considerable negatively related to cognitive-motor functioning. Incoherent results were found for the relationship between NCGS and behavioral/emotional problems, health related quality of life, parenting stress and curiosity. Curiosity was not found to mediate the relationship between NCGS and cognitive-motor functioning. Conclusion: This thesis finds partial support for the negative relationship between NCGS and facets of psychological functioning. Cognitive-motor functioning was found to be negatively related to anti-gliadin IgA and IgG, implying a possible effect of NCGS. A larger sample size and more studies are needed to further investigate the proposed relationship.