The role of maternal risk factors in the development of nausea and vomiting in pregnancy was studied in a historical cohort of 825 women who gave birth at the University of California (Los Angeles) Medical Center during a one-year period (April 1983-March 1984). The roles of demographic factors, reproductive history, and consumption of alcohol and tobacco in affecting the risk of developing nausea and vomiting were studied using both bivariate and multivariate statistical methods. Interpretations of the statistical analyses identify three risk factor associations correlated with decreased risk of nausea and vomiting and one factor associated with increased risk. The most apparent pattern was that women who were ethnically white, of white collar or professional occupation, and who consumed alcohol prior to conception, were at decreased risk for nausea and vomiting. The second pattern of decreased risk consisted of women over 35 years old with a history of infertility for one or more years prior to the current conception. The third low-risk pattern consisted of women without a history of nausea during prior pregnancies. The only factor associated with an increased risk was housewife occupational status. The results of this study are consistent with an endocrinologic model for the etiology of pregnancy-induced nausea and vomiting.