Early Maladaptive Schemas, as measured with the Young Schema Questionnaire (YSQ), are proposed to underlie a variety of mental health problems, in particular Personality Disorders. The latest short version of the instrument measuring all 18 schemas, the YSQ-S3, has only been examined to a limited extent, and its associations with Personality Disorders have not yet been tested in a psychiatric setting. We investigated psychometric properties of the Danish YSQ-S3 including its associations with Personality Disorders. A mixed Danish sample of clinical and nonclinical participants (N = 567) completed the YSQ-S3, whereas a clinical subsample (n = 142) was also assessed with a diagnostic interview for Personality Disorders. We performed reliability analysis, confirmatory factor analysis, regression analysis, and tested for group differences using analysis of variance. The Danish YSQ-S3 proved to be a reliable and valid measure. Its theoretical factorial structure was weakly but sufficiently supported. Its scales were meaningfully associated with specific Personality Disorders and discriminated between relevant groups. We conclude that the YSQ-S3 is a psychometrically valuable instrument for the assessment of Early Maladaptive Schemas in both clinical and research settings. Findings are discussed in relation to Personality Disorders and the Schema Therapy model.