Adverse childhood experiences (ACEs) are common and increase the risk of poor health outcomes. Resilience may offer protection against the impacts of ACEs. This study examined the association between maternal ACEs and mental/behavioral health outcomes during pregnancy overall and by resilience. The sample comprised pregnant patients in two pilot studies screened for eight ACEs and resilience during standard prenatal care in Kaiser Permanente Northern California from 1 March 2016 to 30 July 2016 (Study 1, medical centers A, B) and from 1 April 2018 to 31 March 2019 (Study 2, medical centers A, C). Early pregnancy outcomes included anxiety and depressive disorders, depression symptoms, intimate partner violence (IPV), and substance use. Multivariable logistic regression was used in this cross-sectional study to examine associations between maternal ACEs (0, 1–2, ≥3) and mental/behavioral health outcomes overall and among those with low and high resilience. Patients (n = 1084) averaged 30.8 years (SD 5.1); 41.7% were non-Hispanic White; 41.7% experienced ≥1 ACE, and 40.3% had low resilience. Patients with 1–2 ACEs or ≥3 ACEs (versus 0 ACEs) had higher odds of anxiety and depressive disorders, depressive symptoms, IPV, and any prenatal substance use (OR 1.44–4.40,p< 0.05). Each individual ACE was associated with ≥2 mental/behavioral health outcomes. In stratified analyses, having ≥1 ACE (vs. 0) was associated with a greater number of mental/behavioral health outcomes among patients with low versus high resilience. ACEs were associated with prenatal mental/behavioral health conditions, particularly in the context of low resilience, highlighting the importance of trauma-informed prenatal care and the need to study resilience-building interventions during pregnancy.