We examined the interaction of cognitive styles and life events in predicting the depressive and hypomanic mood swings of 43 undergraduates meeting criteria for a subsyndromal mood disorder (i.e., cyclothymia, dysthymia, or hypomania) or no lifetime diagnosis. Participants completed symptom, cognitive style, and life events measures on three separate occasions as the different mood states characteristic of their subsyndromal disorder naturally occurred. Normal controls were assessed in three separate normal mood states at times yoked to participants in the three disorder groups. All groups' attributional styles and dysfunctional attitudes remained stable across large changes in mood and symptomatology and cyclothymics' cognitive styles were as negative as those of dysthymics. Moreover, hierarchical regression analyses indicated that participants' attributional styles, as measured in a normal mood state (Time 1), in interaction with intervening life events predicted prospectively their depressive symptom changes at Times 2 and 3 and their hypomanic symptom changes at Time 2. These findings provide support for the cognitive vulnerability-stress hypothesis of the Hopelessness theory of depression (Abramson, Metalsky, & Alloy, 1989) and suggest that the logic of the Hopelessness theory's vulnerability-stress hypothesis extends to the prediction of manic/hypomanic symptoms.