Celiac disease is a lifelong autoimmune disease characterized by a specific serological and histological profile, in which gluten intake elicits a cellular and humoral immune response leading to the small intestine mucosa damage. Gluten immunogenic peptides (GIP) are resistant to the digestive tract effects, and are therefore excreted in the stool, indicating patient’s non-adherence to a gluten-free diet. Hypothesis of this dissertation is that the GIP allows more reliable monitoring of gluten-free diet in patients with celiac disease compared to current clinical practice, and better assessment of the dietary adequacy impact on nutritional status, clinic presentation and patient’s quality of life. The objectives of the study were to determine the role of GIP in gluten-free diet adherence in adult patients with celiac disease, and to determine the relationship between adherence to parameters of nutritional status, disease activity and quality of life. The study included 60 adult patients diagnosed with celiac disease and 10 healthy volunteers from the control group of the Department of Gastroenterology and Hepatology, Clinic for Internal Medicine, Clinical Hospital Center Zagreb in 2020. The scientific contribution of cross-sectional research has confirmed the reliable monitoring of gluten-free adherence in patients with celiac disease compared to previous clinical practice. In the assessment of diet adequacy impact on nutritional status, GIP did not show a significant relevance. Based on the results obtained, it can be concluded that the application of GIP for the detection of gluten intake will significantly contribute to better control of adherence to a gluten-free diet.