Adversity experience, in both childhood and adulthood, has been associated with the development of depression. However, it is currently unclear how variation in timing and duration of adversity across childhood and young adulthood affects the extent of depression symptomology. Data were analyzed from 2610 individuals from the National Longitudinal Study of Adolescent to Adult Health in the USA. Adversity in childhood and adulthood was evaluated using instruments similar to the adverse childhood experiences questionnaire, and associations were assessed by Poisson regression. Any adversity experience was associated with significantly elevated depression symptoms in young adulthood. Individuals who experienced adversity during both childhood and adulthood had significantly higher depression symptoms than those experiencing adversity during only childhood or adulthood, suggesting a potential dose-response relationship between duration of adversity experience and depression symptomology. These results suggest that any adversity experience increases depression symptoms in young adulthood and that cumulative adversity is particularly detrimental. While long-term interventions to reduce adversity exposure would be most efficacious, interventions to reduce adversity at any period would still be beneficial.