In a database cohort study, the risk of adverse birth outcome in Danish women who redeemed a fluoroquinolone prescription during pregnancy was examined. Among 87 women who redeemed a fluoroquinolone prescription at any time during the pregnancy, the prevalence ratio of preterm birth was 1.4 (95% confidence interval (CI), 0.6-3.2), one woman had a stillbirth, and no children died during the perinatal period. Among 130 women who redeemed a prescription during the first trimester or 30 days before conception, the prevalence ratio of congenital malformation was 0.7 (95% CI, 0.3-2.0) and the prevalence ratio of bone malformations was 2.2 (95% CI, 0.7-6.7). Our study raises the concern that prenatal fluoroquinolone exposure may be associated with an increased risk of bone malformations.