OBJECTIVES: To describe the discovery and development of the Aberdeen 1921 and 1936 birth cohort studies. STUDY DESIGN: The Aberdeen birth cohort studies were started in 1998 when the Scottish Mental Survey archives of the Scottish Council for Research in Education were re-discovered and permissions granted to follow-up survivors born in 1921 or 1936 and then aged about 77 or 64 years and who had entered (or were about to enter) the age of greatest risk for Alzheimer’s disease (AD). MAIN OUTCOME MEASURES: Sources of attrition from the study, exposures to childhood adversity, nutritional, genetic and life style factors of possible relevance to extent of age-related cognitive decline and the timing of onset of dementia. RESULTS: By 2010, the feasibility of following up more than 75% of Scottish Mental Survey survivors living in the Aberdeen area without dementia was well-established, dementia ascertainment to age about 88 years was completed in the 1921 birth cohort and was underway in the 1936 born cohort. CONCLUSION: These databases are available to other bone fide research groups wishing to test specific hypotheses that may either replicate their own findings or make best use of the data collected in the Aberdeen studies.