The Hospital Anxiety and Depression (HAD) scale is a widely used self-report questionnaire for assessing anxiety and depression. This study evaluated its psychometric properties in a large population (n=51,930) from the Nord-Trondelag Health Study in Norway. Principal component analysis (PCA) revealed a two-factor structure, with anxiety and depression sub-scales accounting for 57% of the variance. The anxiety sub-scale had a Cronbach's α of 0.80, and the depression sub-scale 0.76, indicating good internal consistency. The two sub-scales shared 30% of the variance, with higher correlations in populations with somatic or mental problems. Item 7 of the anxiety sub-scale loaded more on the depression factor, suggesting potential issues with homogeneity. The HAD scale showed robust psychometric properties, including good factor structure, intercorrelation, homogeneity, and internal consistency. The study supports the HAD scale as a reliable instrument for screening anxiety and depression in general populations. However, the scale may have limited coverage of certain depression symptoms, such as hopelessness and guilt, and does not assess somatic symptoms. The study also found that non-participation was more common in men and those aged 40–69, but the factor structure remained stable across different subgroups. The results suggest that the HAD scale has good psychometric properties, making it a useful tool for screening anxiety and depression in various populations.The Hospital Anxiety and Depression (HAD) scale is a widely used self-report questionnaire for assessing anxiety and depression. This study evaluated its psychometric properties in a large population (n=51,930) from the Nord-Trondelag Health Study in Norway. Principal component analysis (PCA) revealed a two-factor structure, with anxiety and depression sub-scales accounting for 57% of the variance. The anxiety sub-scale had a Cronbach's α of 0.80, and the depression sub-scale 0.76, indicating good internal consistency. The two sub-scales shared 30% of the variance, with higher correlations in populations with somatic or mental problems. Item 7 of the anxiety sub-scale loaded more on the depression factor, suggesting potential issues with homogeneity. The HAD scale showed robust psychometric properties, including good factor structure, intercorrelation, homogeneity, and internal consistency. The study supports the HAD scale as a reliable instrument for screening anxiety and depression in general populations. However, the scale may have limited coverage of certain depression symptoms, such as hopelessness and guilt, and does not assess somatic symptoms. The study also found that non-participation was more common in men and those aged 40–69, but the factor structure remained stable across different subgroups. The results suggest that the HAD scale has good psychometric properties, making it a useful tool for screening anxiety and depression in various populations.