Birth outcomes of women with anorexia nervosa are poorly understood. We hypothesized that hospitalization for anorexia nervosa before or during pregnancy is associated with an elevated risk of adverse maternal and infant birth outcomes. We performed a retrospective cohort study of 2,134,945 pregnancies in Quebec, Canada, from 1989 to 2016. The main exposure measure was anorexia nervosa requiring hospital treatment before or during pregnancy. Outcome measures included stillbirth, preterm birth, low birth weight, small-for-gestational age birth, preeclampsia, gestational diabetes, cesarean delivery, and other pregnancy disorders. We computed risk ratios and 95% confidence intervals (CI) for the association between anorexia nervosa and birth outcomes adjusted for maternal characteristics. Compared with no hospitalization, anorexia nervosa hospitalization was associated with 1.99 times the risk of stillbirth (95% CI 1.20-3.30), 1.32 times the risk of preterm birth (95% CI 1.13-1.55), 1.69 times the risk of low birth weight (95% CI 1.44-1.99), and 1.52 times the risk of small-for-gestational age birth (95% CI 1.35-1.72). The associations with low birth weight and small-for-gestational age birth were more prominent in women hospitalized for anorexia nervosa during pregnancy or within 2 years of delivery. Hospitalization for anorexia nervosa was associated with certain maternal outcomes, including precipitate labor, acute liver failure, and admission to an intensive care unit. Hospitalization for anorexia nervosa before or during pregnancy is associated with adverse infant and maternal outcomes. Infants are primarily at risk of stillbirth, preterm birth, low birth weight, and small-for-gestational age birth.