The association of nausea and vomiting in pregnancy with the outcome of pregnancy was investigated in a historical cohort of 903 women in Los Angeles, California, USA. Multivariahle statistical methods were employed to control for the potential confounding effects of age, ethnicity, occupation, and anti-emetic use on pregnancy outcome. The analyses indicated that vomiting was associated with decreased risk of miscarriage (adjusted odds ratio 0·18, 95% CI 0·06 to 0·53); women with nausea but no vomiting had a miscarriage risk equal to that in the sample overall. Among the subsample of women with signs of threatened miscarriage, those who had experienced vomiting had a decreased risk of miscarriage (10·3%vs 31·7% in the subsample). No statistically significant association was observed between nausea and vomiting of pregnancy and other pregnancy outcomes (perinatal mortality, fetal anomalies, neonatal anthropometric measures).