Abstract. The interpersonal reactivity index (IRI) is a widely used personality questionnaire for measuring empathy. We investigated the psychometric properties of the German version using the partial credit model. If this model fits the data, the raw-scores are fair measures of the latent construct. Only in such a case, further analyses based on the raw-scores are accurate and valid. The results showed model fit only for the subscale empathic concern. The subscales perspective taking and fantasy consisted of two theoretically explainable sub-dimensions. For the subscale personal distress, no model fit could be achieved. Our study provides important information on the psychometric qualities of the IRI that has been repeatedly used to assess, for example, group differences. It demonstrates that these analyses were not warranted by the psychometric quality of the questionnaire. Our results provide direct suggestions (e.g., theoretically explainable sub-dimensions) for further developments of the IRI to overcome this limitation.