Background <p>Population ageing has increased the number of very old adults undergoing abdominal surgery. In this group, outcomes beyond mortality and morbidity, including functional status and quality of life, are highly relevant. The EuroQol 5D-3L questionnaire is widely used, but evidence of its psychometric performance in patients aged 80 years and older undergoing surgery remains limited. This study evaluated its measurement properties in this population.</p> Methods <p>A scale validation study was conducted. Health status was measured using the EuroQol 5D-3L questionnaire and its visual analogue scale. Structural validity was examined using exploratory and confirmatory factor analyses based on polychoric correlations. Internal consistency was assessed using Cronbach alpha and McDonald omega. Short-term stability and construct validity were evaluated using agreement coefficients and correlations with depressive symptoms and clinical severity.</p> Results <p>388 patients were included, with a mean age of 84.32 years (SD = 3.4). Factor analyses supported a bidimensional structure separating physical functioning from mental and affective health, with better fit for the two factor model. Internal consistency was Cronbach’s alpha of 0.83 and McDonald’s omega of 0.90. A ceiling effect was observed in 32% of participants. Agreement over 15 days was low for EQ-5D-3L dimensions and absent for overall perceived health measured with the EQ-VAS. Small to moderate correlations with depressive symptoms and weak associations with clinical severity supported construct validity.</p> Conclusions <p>The EQ-5D-3L demonstrated acceptable psychometric performance for assessing self-reported health status in very old surgical patients, supporting its use in clinical evaluation and outcomes research in geriatric surgical care.</p>