OBJECTIVES: The present study in hypomanic and manic patients explored how amygdala responses to affective stimuli depend on the valence of the stimuli presented. METHODS: We compared 10 patients with 10 matched healthy control subjects. We measured blood oxygen level-dependent (BOLD) responses in the amygdala while subjects passively viewed photographs taken from the International Affective Picture System. After the fMRI session, subjects saw the pictures again and subjectively rated the emotional valence and intensity of each picture. RESULTS: Compared to healthy individuals, hypomanic or manic patients showed higher valence ratings in positive pictures and associated larger BOLD responses in the left amygdala during positive versus neutral picture viewing. This enhanced amygdala activation was correlated with Young Mania Rating Scale scores and with euphoric as opposed to irritable symptom presentation. CONCLUSIONS: Increased valence ratings and amygdala responses to positive affective stimuli may reflect a positive processing bias contributing to elevated mood states characteristic for euphoric mania.