Background <p>The ageing process can lead to malnutrition due to a variety of physiological and psychological issues. Investigating nutrition, lifestyle and psychological status is important for improving the health of the geriatric. The aim of this study was therefore to evaluate the relationship between malnutrition, dietary quality and psychological well-being in older adults.</p> Methods <p>One hundred three older adults treated at the Gülhane Training and Research Hospital Geriatrics polyclinic participated in this cross-sectional study. The researchers recorded sociodemographic characteristics, health information, anthropometric measurements, the Short Nutritional Assessment Questionnaire for 65 + (SNAQ⁶⁵⁺) screening test, the Mediterranean Diet Adherence Scale (MEDAS) and the Psychological Well-Being Scale for the Older People (YPIOA) using a questionnaire during face-to-face interviews. Generalised Anxiety Disorder-7 (GAD-7) test was administered to older adults who applied to the geriatrics outpatient clinic at the time of application; individuals who did not meet the criteria were excluded from the study.</p> Results <p>The results of the study showed that the psychological well-being scale scores of individuals who strictly adhered to the Mediterranean diet (mean = 68.1) were significantly higher than those of individuals who did not adhere to the Mediterranean diet (mean = 59.5)(<i>p</i> &lt; 0.05). Linear regression was used to evaluate older adults according to their MEDAS and YPIOA values. The test results revealed a significant positive correlation between the MEDAS score and the YPIOA (<i>p</i> &lt; 0.05). However, no significant difference was found between the groups when the relationship between the MEDAS and SNAQ⁶⁵⁺ scores of older adults was evaluated (<i>p</i> &gt; 0.05).</p> Conclusion <p>According to the results of the study, geriatric people who scored higher on the MEDAS also scored higher on the YPIOA. However, no significant relationship was found between SNAQ⁶⁵⁺ and MEDAS scores. These findings suggest that the quality of an individual's diet may affect not only their physical health, but also their psychological well-being. Therefore, treatment plans for the nutritional needs of older adults should take into consideration not only energy and nutrient intake, but also the individual's lifestyle, habits and psychological status.</p> Graphical Abstract <p></p>