There has been considerable debate about the diagnostic rules for bipolar II disorder, particularly the 4-day duration criteria for hypomanic episodes. This study examined whether highs lasting minutes or hours differed from longer highs in terms of clinical features and symptom severity. It also examined whether duration of highs predicted bipolar disorder being diagnosed.

A total of 518 subjects with significant episodes of depression and ‘highs’ completed a web-based self-report questionnaire. Those who reported their longest highs lasting minutes or hours were compared with those who reported longer durations of highs on a range of clinical variables and measures of symptom severity.

Subjects whose highs lasted minutes or hours reported clinical features and severity of symptoms similar to those whose highs lasted 3–7 days. However, the odds of being diagnosed with bipolar disorder for those with highs lasting 3–7 days were almost three times higher than for those whose highs lasted minutes or hours.

The 4-day DSM-IV minimum-duration criteria for hypomania may lead to failure to diagnose subjects with brief highs who have true bipolar disorder and thus should be reconsidered.