Purpose: This study is dedicated to the statistical analysis of a new, not yet sufficiently validated self-assessment tool, the Hypomania self-rating scale (HSRS), with the objective of testing its usefulness for the research of hypomanic episodes and symptoms. The focus of the study is on the statistical reliability of the questionnaire in differentiating between two diagnostic groups: depressive and bipolar. The findings of this study are additionally compared with the results of existing preliminary investigations conducted in Sweden and Italy. Method: The sample consists of 132 out-patients, who at the time the survey was conducted were receiving ambulant treatment from the psychiatric clinic of the Martin-Luther University Halle-Wittenberg or from a private practise. Subjects were classified using patient records into the two diagnostic groups, and the classification was independently confirmed by an experienced clinician. Results: The responses of the two groups differed significantly in several questions of the self-rating scale. The answers to a 32-question subscale of the questionnaire (HCL-32) also showed a correlation to the established diagnoses. As in the two preliminary investigations, the factor-analysis of the subscale identified a two-factor variation. Conclusion: The long-term goal of working with the HSRS questionnaire is its improvement, shortening and validation. The data obtained in this study have shown that the questionnaire is statistically reliable in differentiating between the two diagnostic groups. In comparison to the other self-rating scales, the HSRS has the advantage that hypomanic episodes, along with their consequences, can also be investigated retrospectively and over time. The study at hand, however, does not represent a systematic, statistical treatment of the questionnaire; a complete validation of the HSRS is subject to further study.