The Harmonized Diagnostic Assessment of Dementia for the Longitudinal Aging Study in India (LASI-DAD) is an add-on study to the Longitudinal Aging Study in India (LASI) focused on late-life cognition and dementia. LASI is an ongoing, multi-purpose cohort study of 72,000 community-residing older adults aged 45 and older and their spouses regardless of age, with an oversample of persons aged 65 and above. Using the Census as the sampling frame, LASI was representative of both the nation as a whole and each state and union territory. LASI-DAD also drew a nationally representative, sub-sample of 4,096 LASI participants aged 60 and above and administered an in-depth cognitive test battery and informant interview that is harmonized with the U.S. Health and Retirement Study and its sister studies around world.