The BDLONG Study is a pilot longitudinal neuroimaging and digital phenotyping project at the University of Pittsburgh, including 16 participants (11 with bipolar I/II disorder and 5 healthy controls) from the Pittsburgh, Pennsylvania area in the United States of America. Participants with bipolar disorder were recruited through the Child and Adolescent Bipolar Services (CABS) clinic, while healthy controls were recruited via the Pitt+Me research registry, with recruitment beginning during the COVID-19 pandemic. The bipolar cohort consisted of adolescents and young adults aged 13 to 30 years, each with at least one depressive and one manic, hypomanic, or mixed episode in the past year, while the healthy control cohort was age-matched with no psychiatric diagnoses or family history of bipolar disorder. The participants contributed 70 fMRI scans altogether. Youth with bipolar disorder were followed for 4 to 6 fMRI scans across nine months with weekly mood questionnaires, while healthy controls completed four scans at approximately 12-week intervals.