<h3>Study Objective</h3> To retrospectively investigate prevalence of adverse obstetric and neonatal outcomes in women with histopathologically proven adenomyosis compared to the general (Dutch) population. <h3>Design</h3> Retrospective population-based cohort study. <h3>Setting</h3> Population-based national databases. <h3>Patients or Participants</h3> Women with registered pregnancy outcomes in the Dutch national Perined registry, who received a histopathological diagnosis of adenomyosis (post-hysterectomy) between 1995 to 2018, as registered in the Dutch national pathological registry, were included. Pregnancy outcomes of 7,925 women with a histopathological diagnosis of adenomyosis were compared to 4,615,803 women without adenomyosis. Adjusted Odds Ratios (aOR, 95% CI) were calculated. Outcomes were corrected for: maternal age, parity, ethnicity, year of registered birth, induction of labor, hypertensive disorder in previous pregnancy, multiple gestation and low socioeconomic status. <h3>Interventions</h3> Hysterectomy. <h3>Measurements and Main Results</h3> Women with adenomyosis had an aOR of 1.370 (95% CI 1.25-1.498) for hypertensive disorders, an aOR of 1.373 (95% CI 1.248-1.510) for preeclampsia, and aOR of 1.15 (95% CI 1.067-1.248) for small-for-gestational-age. Women with adenomyosis had an aOR of 1.538 (95% CI 1.410-1.679) for emergency caesarean delivery, an aOR of 1.242 (95% CI 1.124-1.373) for failure to progress in labor, an aOR of 1.278 (95% Ci 1.101-1.484) for placental retention and an aOR of 1.232 (95% CI 1.098-1.383) for postpartum hemorrhage. There was no significantly increased risk for HELLP, eclampsia, placental abruption, operative vaginal delivery or need for oxytocin stimulation. <h3>Conclusion</h3> This is the largest study up to now which investigates the impact of adenomyosis on obstetric outcomes and is the first study which uses the golden standard of adenomyosis diagnosis: histopathology. We confirm women with adenomyosis show an increased prevalence of a variety of adverse obstetric outcomes, specifically hypertensive disorders of pregnancy, small-for-gestational age, failure to progress in labor and placental retention. We conclude that uterine placental invasion and contractile function in labor may be impaired in women with adenomyosis.