AIMS: Amoxicillin is a widely used penicillin, but data on its safety in pregnancy are limited. We examined the association between amoxicillin exposure during pregnancy and birth weight, preterm delivery, congenital malformations, perinatal death, and spontaneous abortion. METHODS: We identified all primiparous women with a live birth, or a stillbirth after the 28th gestational week, from 1 January 1991-31 December 2000 in the County of North Jutland, Denmark. Data on prescriptions for amoxicillin and outcome were obtained from population-based registries. Using a follow-up and a case-control design, we compared pregnancy outcomes between women who had been prescribed amoxicillin during pregnancy and those who had not, adjusting for available potentially confounding factors. RESULTS: We identified 401 primiparous women who redeemed a prescription for amoxicillin during their pregnancy. The control group consisted of 10 237 primiparous women who did not redeem any prescriptions from 3 months before pregnancy until the end of pregnancy. The adjusted mean birth weight of children born to amoxicillin-exposed mothers was 57 g [95% confidence interval (CI) 9, 105] higher than that of children born to controls. Odds ratios among amoxicillin-exposed relative to controls were: low birth weight 0.63 (95% CI 0.26, 1.53), preterm delivery 0.77 (95% CI 0.49, 1.21), congenital malformation 1.16 (95% CI 0.54, 2.50), and spontaneous abortion 0.89 (95% CI 0.66, 1.18). We did not observe any cases of perinatal death in the amoxicillin-exposed women. CONCLUSIONS: We did not find any increased risk of adverse pregnancy outcome associated with amoxicillin exposure during pregnancy, but additional studies are warranted.