ObjectivesThis paper aims to study dysfunctional self‐schematic processes, abnormal coping styles, over‐responsiveness to reward stimuli (indicative of an over‐sensitive behavioural activation system) and stability of self‐esteem in relation to subclinical hypomania.DesignThree cross‐sectional studies were conducted on selected students on the basis of their scores on the Hypomanic Personality Scale (HPS) (study 1) and on elevated HPS and Dysfunctional Attitude Scale scores (studies 2 and 3).MethodsIn studies 1 and 2, participants completed questionnaires and kept a self‐esteem diary for 6 days. In study 3, the experience sampling method was used to assess momentary self‐esteem, emotion and use of different coping styles over a 6‐day period.ResultsStudy 1 demonstrated that hypomanic traits are associated with high fluctuations in self‐esteem. In study 2, high scores on both the HPS and the Dysfunctional Attitude Scale, but not the HPS alone, were associated with bipolar spectrum symptoms. These participants showed more evidence of alcohol and substance abuse, greater self‐esteem fluctuation and dysfunctional coping styles (rumination and risk‐taking) compared with controls. Changes in self‐esteem were related to the use of these strategies.ConclusionsVulnerability to bipolar disorder is associated with a combination of depression‐related and reward‐related processes. Copyright © 2011 John Wiley & Sons, Ltd.