Background <p>Life-threatening conditions such as cancer can evoke demoralization, which is characterized by feelings of meaninglessness, hopelessness, and helplessness. Assessing demoralization in cancer patients is crucial. This study aimed to evaluate the psychometric properties of the Turkish version of the Demoralization Scale-II (TDS-II) and explore its relationship with sociodemographic and disease-related factors.</p> Methods <p>This study included 287 cancer patients, 265 of whom completed the final analysis. The participants completed the TDS-II, the Patient Health Questionnaire-9 (PHQ-9), and the Generalized Anxiety Disorder Questionnaire-7 (GAD-7). The psychometric evaluation of the TDS-II involved assessments of convergent, construct, and discriminant validity and internal consistency.</p> Results <p>Structural validity analysis indicated that both single-factor and two-factor models demonstrated comparable model fit, with CFI and NFI values ranging from 0.903 to 0.944 and SRMR values below 0.05. However, internal discriminant validity was not supported, as the average variance extracted (AVE) values for each factor in the two-factor model were lower than the square of their correlation coefficient. Strong correlations between the TDS-II and the, PHQ-9 and GAD-7 supported convergent validity. The internal consistency was high, with a Cronbach’s alpha of 0.93 for the TDS-II. Demoralization scores were significantly higher among women, patients with a family history of cancer, and those with stage IV disease.</p> Conclusions <p>The Turkish version of the Demoralization Scale-II (TDS-II) is reliable for assessing demoralization in cancer patients and has strong psychometric properties. Screening for demoralization in high-risk groups may help prevent the progression of long-term psychological disorders.</p>