We discuss the Hypomanic Personality Scale (Hyp; Eckblad & Chapman, 1986) and the Behavioral Inhibition System (BIS–BAS; Carver & White, 1994) and Behavioral Activation System (BAS; Gray, 1991) Scales as risk factors for bipolar disorders. The dysregulation of the BAS is considered to be central and results in higher variability in mood. Therefore, we examined how those scales are associated with mood fluctuations. A total of 59 participants completed a diary for at least 17 days. It included a modified Center for Epidemiologic Studies–Depression Scale (Meyer & Hautzinger, 2001) assessing depression and mania and the Positive and Negative Affect Schedule (Watson, Clark, & Tellegen, 1988). Hyp and BAS predicted levels of mania and of positive affect but also fluctuations of mania. Hyp also predicted instability of negative affect. Our data also suggest that mood variability is a trait-like feature. Both scales seem not to be perfect measures of the dysregulation factor. Future research should assess this dysregulation more directly.