Factors associated with early pregnancy vomiting were investigated in 9098 first-trimester registrants in the Collaborative Perinatal Project. Vomiting in the absence of hyperemesis or gastroenteritis was noted in 56% of all women, and was more common among primigravidas (P = .002), younger women (P less than .001), women with less than 12 years of education (P less than .001), nonsmokers (P less than .001), and women weighing 77.1 kg (170 lb) or more (P = .003). Adjustment for confounders did not change these associations. Women reporting vomiting were less likely to experience miscarriage or stillbirth (P = .002) and delivery before 37 weeks' gestation (P = .004), but there was no difference in infant birth weight between mothers with and without vomiting (P = .48). Women who vomit in one pregnancy are more likely to vomit in subsequent pregnancies than are comparable women who did not vomit.