Background: Psychological distress is a trans-diagnostic feature of mental suffering closely associated with mental disorders. Kessler’s 10-item Psychological Distress Scale (K10), a scale with sound psychometric properties, is widely used in epidemiological studies. Aim: To translate and investigate whether K10 is a reliable and valid rating scale for the measurement of psychological distress in a Danish population. Methods: The translation was carried out according to official WHO translation guidelines. A sample of 100 subjects was included, 54 patients from the regional Mental Health Service (MHS) and 46 subjects with no psychiatric history. All participants were assessed with a psychiatric diagnostic interview (MINI) and handed out K10. Concurrent validity was assessed by WHO Well-being Index (WHO-5). Correlation matrix analysis was conducted for the full sample and receiver operating characteristic (ROC) curves for discriminating mental health service affiliation. Results: Mean K10 scores differed, with decreasing levels, between inpatients and outpatient in MHS and the subjects with no psychiatric history. Factor analysis confirmed a unidimensional structure, and Cronbach’s alpha and Omega showed excellent internal reliability. AUC for the K10 ROC curves showed excellent sensitivity (0.947 [0.900–0.995]), accurately differentiating mental health from non-mental health patients. Conclusion: The Danish K10 has the same strong internal reliability as the original English version, and scores differ between psychiatric patients in outpatient and emergency ward settings. Clinical implications: The Danish K10 translation is authorized and freely available for download at https://www.hcp.med.harvard.edu/ncs/k6_scales.php. The utility as an instrument for clinical screening in a mental healthcare setting is supported.