Since the introduction of bipolar II disorder (BP-II) into the DSM-IV system, there have been studies to identify characteristics of BP-II, challenging the notion that BP-II is merely a milder form of bipolar I disorder (BP-I). Despite of suggested high prevalence rate and unfavorable prognosis of BP-II, still little is clarified about clinical and biological correlates of BP-II which render more solid diagnosis and treatment. Here we present data from clinical researches in Korea to suggest and stimulate the idea about pathophysiology of BP-II. Conventional neurocognitive function tests suggest that patients with BP-II showed less deficits in memory and executive functions than patients with BP-I. Semantic categorization was well organized in patients with BP-II than BP-I. Multivariate analyses of symptom structure revealed that inter-episodic residual symptoms of clinically stable patients with BP-II showed clearer separation between cognitive and emotional symptom domains compared to patients with BP-I. Neuroimaging data showed limited abnormalities in patients with BP-II, compared to widespread gray and white matter alterations in patients with BP-I. Comorbidity data showed that BP-II was associated with higher rate of comorbid anxiety disorders than BP-I. Taken together, our data suggest that BP-II may be mainly associated with disturbances of affective processing compared to more generalized alterations in BP-I. Further researches are justified to test speculations from these limited evidence and experiences.