Background <p>Gratitude has been increasingly studied as a key psychological strength associated with subjective well-being, positive interpersonal relationships, and mental health. The assessment of gratitude through validated instruments is essential for both research and clinical practice. Although the Gratitude Questionnaire 6 items (GQ-6) is widely used in various cultural contexts, there is a need to evaluate its psychometric properties and cultural relevance in Portuguese-speaking populations, particularly among adults.</p> Objective <p>The present study aimed to examine the psychometric properties and validity evidence of the Portuguese version of the Gratitude Questionnaire, with a focus on its internal structure, score reliability, and evidence based on relations to other variables.</p> Methods <p>A final sample of 810 Portuguese adults (Mage = 43.79; SD = 23.69) completed the Portuguese version of the GQ-6. Exploratory factor analysis and confirmatory factor analysis were conducted to evaluate the instrument’s internal structure. A subsample of 362 adults completed the revised 5-item version (GQ-5), along with measures of life satisfaction and loneliness, to assess evidence based on relations to other variables.</p> Results <p>Findings supported a one-factor structure, with the 5-item version showing a better model fit than the original 6-item scale. The GQ-5 demonstrated significant positive correlations with life satisfaction and negative correlations with loneliness, supporting this source of validity evidence. The instrument also exhibited adequate internal consistency.</p> Conclusion <p>The Portuguese version of the GQ-5 is a psychometrically sound and culturally appropriate measure for assessing gratitude in adult populations.</p>