Objectives. Patients affected by bipolar disorder (BP) and major depressive disorder (UP) share the susceptibility to experience depression and differ in their susceptibility to mania, but clinical studies suggest that the biological substrates of the two disorders could influence the apparently similar depressive phases. The few brain imaging studies available described different brain metabolic and neural correlates of UP and BP. Methods. We studied the BOLD neural response to a moral valence decision task targeting the depressive biases in information processing in 36 subjects (14 BP, 11 UP, and 11 controls). Results. Main differences between UP and controls and between UP and BP were detected in left ventrolateral prefrontal cortex (PFC, BA 47). Neural responses of BP patients differed from those of control subjects in multiple brain areas, including anterior cingulate cortex (ACC) and medial PFC, bilateral dorsolateral PFC, temporal cortex and insula, and parietal and occipital cortex. Conclusions. Our results are in agreement with hypotheses of dysfunctions in corticolimbic circuitries regulating affects and emotions in mood disorders and suggest that specific abnormalities, particularly in ventrolateral PFC, are not the same in UP and BP depression.