In bipolar-II (BP-II) disorder impulsivity (defined as excessive risky activities by DSM-IV-TR) is one of the symptoms of hypomania. It is unclear if impulsivity is also a trait in BP-II.

The aim was to test if impulsivity was also a trait in BP-II.

Consecutive 136 remitted BP-II outpatients (assessed when presenting for depression by a mood disorder specialist psychiatrist using the Structured Clinical interview for DSM-IV), self-assessed trait impulsivity during follow-ups, using the Personality Questionnaire of the Structured Clinical interview for DSM-IV Axis II Disorders, in a private practice. Trait mood swings were also self-assessed, using the TEMPS-A. A trait nature of impulsivity in BP-II could be supported by finding (1) a relatively high frequency, (2) association between trait impulsivity and symptoms of past hypomania, especially impulsivity, (3) dose–response relationship between number of past hypomania symptoms and trait impulsivity, and (4) association between trait impulsivity and trait mood swings (a trait feature of BP-II).

Trait impulsivity was present in 41.1% of BP-II. BP-II with, versus BP-II without, trait impulsivity had significantly more males, trait mood swings, past hypomania symptoms (irritable mood, talkativeness, increased goal-directed activity), and excessive risky activities (i.e. state impulsivity), corresponding to an irritable risky overactivity. Past state impulsivity and trait impulsivity were significantly associated. Number of past hypomania symptoms and trait impulsivity were significantly correlated. A dose–response relationship was found between number of past hypomania symptoms and trait impulsivity.

Findings suggest that trait impulsivity may be a feature of BP-II. Limitation of self-assessment of personality traits should be taken into account. Findings may have treatment impacts, as the combination of trait impulsivity and mood swings may facilitate relapses and mixed states, which mood stabilising agents could prevent/delay.