<p>Existential concerns, including fears of death, isolation, identity, and meaning, become salient in late life and affect mental health. This study compared three competing models for the Existential Concerns Questionnaire (ECQ), a 22–item scale assessing existential distress: a unidimensional model, a three correlated factors model (General Existential Anxiety, Death Anxiety, and Avoidance), and a second–order model. Participants were 315 Spanish older adults (134 men, 42.54%, and 181 women, 57.46%), aged 65–93 years (<i>M</i> = 70.53, <i>SD</i> = 4.61). The ECQ was administered alongside the Meaning in Life Questionnaire–Presence subscale, Satisfaction With Life Scale, Psychological Well–Being stress subscale, and Geriatric Depression Scale. Confirmatory factor analyses showed that the three correlated factors model and the second–order model fit excellently and equivalently, whereas the unidimensional model fit less well. Guided by theoretical coherence and parsimony, the second–order model was retained. The ECQ showed strong overall and second–order reliability, though the Avoidance factor and low AVE values suggested the need for refinement at the subscale level. Validity evidence based on internal structure was supported: existential concerns correlated negatively with meaning and life satisfaction, whereas positively with stress and depression. The ECQ demonstrate invariance across gender and age groups. The ECQ proved reliable for detecting existential distress and guiding interventions among older people.</p>