Compelling evidence is now available that adverse childhood experiences are associated with adult pathology. However, understanding of the pathways and mechanisms underlying these associations is limited. Participants in the European Prospective Investigation into Cancer and Nutrition in Norfolk, UK (EPIC-Norfolk), aged 40 to 80 years, provided an opportunity to investigate the hypothesis that adverse experience in childhood is associated with peripheral leukocyte count in adulthood in the context of a large-scale population-based cohort study. White blood cell counts were available from 11,367 participants and, after a mean interval of 44 months, from 11,857 at a second health check. A self-completion questionnaire that included the assessment of adverse experience during childhood was administered during the interval between health checks. Associations were observed between early adverse experiences and lymphocyte counts at both health checks. Lifestyle factors accounted for about half of this association. Caution is needed in the interpretation of these findings that require replication but they may be seen to aid understanding of the mechanisms through which early environmental exposures act.