AIM: To investigate the prevalence of undernutrition, risk of malnutrition and obesity in the Italian gastroenterological population. METHODS: The Italian Hospital Gastroenterology Association conducted an observational, cross-sectional multicenter study. Weight, weight loss, and body mass index were evaluated. Undernutrition was defined as unintentional weight loss > 10% in the last threesix months. Values of Malnutrition Universal Screening Tool(MUST) > 2, NRS-2002 > 3, and Mini Nutritional Assessment(MNA) from 17 to 25 identified risk of malnutrition in outpatients, inpatients and elderly patients, respectively. A body mass index ≥ 30 indicated obesity. Gastrointestinal pathologies were categorized into acute, chronic and neoplastic diseases. RESULTS: A total of 513 patients participated in the study. The prevalence of undernutrition was 4.6% in outpatients and 19.6% in inpatients. Moreover, undernutrition was present in 4.3% of the gastrointestinal patients with chronic disease, 11.0% of those with acute disease, and 17.6% of those with cancer. The risk of malnutrition increased progressively and significantly in chronic, acute and neoplastic gastrointestinal diseases in inpatients and the elderly population. Logistical regression analysis confirmed that cancer was a risk factor for undernutrition(OR = 2.7; 95%CI: 1.2-6.44, P = 0.02). Obesity and overweight were more frequent in outpatients. CONCLUSION: More than 63% of outpatients and 80% of inpatients in gastroenterological centers suffered from significant changes in body composition and required specific nutritional competence and treatment. METHODS: The Italian Hospital Gastroenterology Association conducted an observational, cross-sectional multicenter study. Weight, weight loss, and body mass index were evaluated. Undernutrition were defined as unintentional weight loss> 10% in the last threesix months. Values ​​of Malnutrition Universal Screening Tool (MUST)> 2, NRS-2002> 3, and Mini Nutritional Assessment (MNA) from 17 to 25 identified risk of malnutrition in outpatients A total of 513 patients participated in the study. The prevalence of undernutrition was 4.6% in outpatients and 19.6% inpatients. Moreover, undernutrition was present in 4.3% of the gastrointestinal patients with chronic disease, 11.0% of those with acute disease, and 17.6% of those with cancer. The risk of malnutrition increased progressively and significantly in chronic, acute and neoplastic gastrointestinal diseases in in patients and the elderly population. Logistical regression analysis confirmed that cancer was a risk factor for Obesity and overweight were more frequent in outpatients. CONCLUSION: More than 63% of outpatients and 80% of inpatients in gastroenterological centers suffered from significant changes in body composition and required specific nutritional competence and treatment.