346 be an important dimensional aspect of brief hypomania. The current study cannot address whether decreasing the minimum length criterion for an episode of hypomania would improve the accuracy of the diagnosis of bipolar disorder. While most of the hypomania reported in this study was brief and self-limited, in a sample of patients who are all receiving treatment, the high frequency of hypomanic symptoms occurring outside of a DSM-IV episode is troublesome. Although some patients, especially with bipolar II disorder, report improved functioning when experiencing mild hypomania [20, 21], subsyndromal or residual symptoms of mania are associated with an increased risk of relapse [22, 23]. Furthermore, cumulative morbidity in bipolar disorder, even from mild symptoms, may be associated with more functional impairment than the total number of episodes [12, 24, 25]. Hypomania is associated with a high risk for divorce [3], and over a lifetime, an increased use of health services, an increased need for social welfare, and an increase in suicidal behaviors [6]. Clinicians should probe patients with bipolar disorder for brief hypomanic episodes, and assess whether these are interfering with everyday functioning. One clin- ical beneﬁt of daily charting may be to improve the detection and monitoring of subsyndromal mood symptoms. As found in our earlier study [4], there was no signiﬁ- cant difference in the occurrence of 1-day hypomania between patients with bipolar I and bipolar II disorders. Additionally, there were no signiﬁcant demographic dif- ferences between patients who met the 4-day length crite- rion and those who only experienced a hypomanic episode with a shorter length criterion. It does not appear that either experiencing brief hypomanic episodes or single days of hypomania are useful parameters for distinguishing sub- groups within a sample of patients who meet the DSM-IV criteria for bipolar disorder. There are several limitations to this analysis. With a naturalistic design, the patients in this sample varied in disease severity, phase of illness and medications taken. All mood ratings used in this analysis were self-reported, and the ChronoRecord mood rating does not measure the speciﬁc components of hypomania/mania or depression. While a ChronoRecord rating of mania/hypomania best reﬂects activation levels [13], this is not a speciﬁc measure of overactivity which may be a core feature of hypomania [2, 8, 26]. Additionally, clinical diagnosis of a hypomanic episode traditionally emphasizes behavioral manifestations and functional impairment. Daily access to a home com- puter was required throughout the study. However, the demographic proﬁle of the patients who use ChronoRecord is similar to that in other studies of bipolar disorder [12]. This study did not include patients with bipolar disorder 123 Eur Arch Psychiatry Clin Neurosci (2011) 261:341–347 who were not receiving treatment, and patients who never experience hypomania that lasts for 4 days. Finally, this study did not address the issues of differentiating brief hypomania from normal mood elevation, or bipolar disor- der from unipolar depression. In conclusion, decreasing the episode length criterion for hypomania will signiﬁcantly increase the number of patients with episodes and the aggregate number of epi- sodes. Frequency may be an important dimensional aspect of brief hypomania. Decreasing the episode length criterion was not useful for distinguishing subgroups within this sample. Clinicians should probe patients with bipolar dis- order for brief hypomanic episodes. 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