Purpose Growing evidence suggests that prospective informant-reports and retrospective self-reports of childhood maltreatment may be differentially associated with adult psychopathology. However, it remains unknown how associations for these two maltreatment reporting types compare when considering functional outcomes. The present study compared associations between childhood maltreatment and functional outcomes at age 18 years using these two methods. Methods We used data from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative birth cohort of 2232 children born in England and Wales in 1994–1995. Maltreatment prior to age 12 years was assessed prospectively (during multiple home visits between birth and age of 12 years based on interviews with caregivers, researcher observations, and information from practitioners where child protection referrals were made) and retrospectively (at age 18 via self-report on the Childhood Trauma Questionnaire). Nine functional outcomes were measured at age 18, forming two variables capturing: (i) psychosocial and (ii) vocational disadvantage. Results Among the 2054 participants with available data, childhood maltreatment was associated with poorer functional outcomes regardless of whether this was reported only prospectively, only retrospectively, or both. Stronger associations with psychosocial disadvantage arose in the context of retrospective recall by participants (OR = 8.25, 95% CI 4.93–13.82) than prospective reports by informants (OR = 2.03, 95% CI 1.36–3.04) of maltreatment. Conversely, associations with vocational disadvantage were comparable for both prospective informant-reports (OR = 2.19, 95% CI 1.42–3.38) and retrospective self-reports (OR = 1.93, 95% CI 1.33–2.81) of maltreatment. Conclusion Results highlight the importance of considering the maltreatment report type used when interpreting the functional consequences of childhood maltreatment.