It is still under debate whether the reported effects of opioid maintenance therapy (OMT) on child behaviour are a direct effect of prenatal exposure, or whether other factors are involved. This prospective cohort study investigated three models: the teratogenic risk model, the maternal risk model, and a combined risk model in a group of 35 children (M?=?52.20 months, SD?=?1.69) prenatally exposed to OMT. Results revealed support for the maternal risk model and the combined model, with the combined model predicting child internalising and externalising behaviour problems the best (R[superscript 2]?=?0.65, p?=?0.008 and R[superscript 2]?=?0.74, p?=?0.003, respectively). Findings suggest that behaviour problems in children of women in OMT may not be a direct exposure effect. This underscores the importance of taking into consideration multiple factors when studying the effects of prenatal OMT exposure on child behaviour.