BACKGROUND AND OBJECTIVES: Opioid maintenance treatment (OMT), with methadone or buprenorphine, is a key approach for managing opioid use disorder (OUD) during pregnancy. Despite buprenorphine’s superior short-term outcomes, its long-term effects remain understudied. This study aims to evaluate the effects of prenatal OMT exposure on the incidence of childhood neurodevelopmental disorders (NDDs) considering timing effect.