Given the clinical and scientific relevance of dissociative experiences our study aimed to assess the psychometric properties of a short version of the German Dissociative Experience Scale (called FDS-20) as well as its ability to measure changes in dissociation. In a large sample (N = 1289) the FDS- 20 showed good internal consistency. A factor analysis indicated that the scale measures one single factor reflecting the general degree of dissociative psychopathology. Between-group-comparisons suggested a good discriminant validity between high and low dissociators; however, due to high standard deviations the FDS-20 is not well suited for an individual diagnosis and therefore, it should be used as a screening device. Low effect sizes (d < 0,3) between scores at the beginning and the end of inpatient treatment as well as low micro -indices pointed to a temporal stable construct and a trait scale, respectively. Alternatively to group comparisons, individual parameters of treatment success (statistical and clinical significance) were calculated. They proved to be more appropriate in measuring changes in dissociation.