Background This paper reports two studies concerned with the development and validation of the Hypomania Interpretations Questionnaire (HIQ) designed to assess positive self-dispositional appraisals for hypomania-relevant experiences. Methods Study 1: 203 late adolescent participants completed the HIQ along with additional measures of general symptom interpretation, dysfunctional attitudes and hypomanic personality. Study 2: 56 adults with a self-reported diagnosis of bipolar disorder and 39 controls completed a revised HIQ and a measure of current mood symptoms. Results Study 1: The final 10 item HIQ had two subscales: a) positive self-dispositional appraisals (HIQ-H); and b) normalising appraisals (HIQ-NE). Internal and test–retest reliability were adequate. Hypomanic personality scores were significantly and uniquely predicted by recent hypomania-relevant experiences and HIQ-H score. Study 2: HIQ remained internally reliable within this sample. Bipolar participants (BD) reported more subsyndromal mood symptoms than controls (C) and scored significantly higher on HIQ-H even after covarying for these. HIQ-H was the primary predictor of diagnostic group. Its ability to discriminate BD from C was confirmed by ROC analysis. Limitations The studies are cross-sectional and did not include non-bipolar psychiatric control groups. Conclusions HIQ appears to be a reliable and valid measure for the assessment of positive self-dispositional appraisals which seem to be linked to both hypomanic personality and bipolar disorder. The relevance of such appraisals for symptom exacerbation, relapse and psychological treatment would merit future investigation.