PurposeOne in 1,000 pregnancies is complicated by malignancies. Prevalence is greater for benign neoplasms. Adverse outcomes among women with malignancies have been reported. Less is known of postpartum outcomes for infants, or outcomes among women with benign neoplasms.MethodsWe conducted a population-based cohort study using Washington State-linked vital-hospital discharge records. Women with neoplasms (707 malignant; 13,156 benign) with deliveries in 1987–2012 were identified, and a randomly selected comparison cohort. Obstetrical/infant outcomes and rehospitalization < 2 years post-delivery were compared separately for each group by multivariable regressions to estimate risk ratios (RR) and 95% confidence intervals (CI).ResultsWomen with either condition had increased anemia, cesarean, and preterm delivery; their infants were more often < 2,500 g or jaundiced. Women with benign conditions had increased gestational diabetes (RR = 1.20; 95% CI 1.12–1.28) and preeclampsia (RR = 1.27; 95% CI 1.18–1.36); their infants had increased malformations (RR = 1.29; 95% CI 1.19–1.38). Women with neoplasms more often were hospitalized seven or more days or rehospitalized; their infants’ hospitalizations were also longer.ConclusionMalignant and benign neoplasms were associated with several adverse outcomes. Reasons for relationships of benign neoplasms with gestational diabetes, preeclampsia, and congenital malformations merit further study.