Bipolar disorder (BD) is a debilitating psychiatric disorder characterized by fluctuating periods of depression and mania. Researchers have long suspected that BD may be accompanied by abnormal structural and functional changes in the brain. Small cross-sectional brain imaging studies of people with BD have shown hints at those changes, but the ability to interpret data collected at a single timepoint is limited. Now, a multi-center longitudinal study shows aberrant changes over time in the brains of people with BD. Some changes were specifically associated with more episodes of mania.