Objective Exposure to adverse childhood experiences (ACEs) is associated with a broad range of mental health-related outcomes. Previous studies tended to use retrospectively reported ACEs, measure mental health outcomes at a one time point in adulthood and focus on individual outcomes. Hence, this study aimed to examine the association between prospectively and retrospectively measured ACEs and a wide range of mental health-related outcomes, spanning ages 16 to55, using a prospective birth cohort, representative of those born around 1958 in Great Britain. Methods The study used the 1958 National Child Development Study (n ​= ​7980). Adverse childhood experiences were measured both prospectively and retrospectively, and combined into ACE scores. The associations between the ACE scores and mental health were quantified with linear regression for continuous and robust Poisson regression for binary outcomes. Results We found a dose-response association between prospectively and retrospectively reported ACEs and all studied mental health-related outcomes, after accounting for multiple covariates. Among those with 2+ (vs 0) prospective ACEs, the risk of clinically significant psychological distress was up to 2.14 times higher, and of seeing a mental health specialist up to 2.85 times higher. Conclusions Our findings reiterate the need for early-life interventions to reduce inequalities in mental health.