Significance Characterizing the abnormalities in sleep and activity that are associated with bipolar disorder (BP) and identifying their causation are key milestones in unraveling the biological underpinnings of this severe and highly prevalent disorder. We have conducted the first systematic evaluation of sleep and activity phenotypes in pedigrees that include multiple BP-affected members. By delineating specific sleep and activity measures that are significantly heritable in these families, and those whose variation correlated with the BP status of their members, and by determining the chromosomal position of loci contributing to many of these traits, we have taken the first step toward discovery of causative genetic variants. These variants, in turn, could provide clues to new approaches for both preventing and treating BP.