ObjectiveTo test the hypothesis that infection withHelicobacter pyloriis associated with hyperemesis gravidarum.MethodsFrom January 1995 to November 1996 we enrolled 105 patients with hyperemesis gravidarum in a prospective study. The Helicobacter serum Immunoglobulin (Ig) G concentrations in these patients were compared with those in asymptomatic gravidas matched for week of gestation.ResultsPositive serum IgG concentrations were found in 95 of the 105 hyperemesis patients (90.5%) compared with 60 of 129 controls (46.5%). A χ2test showed statistical significance (P< .001). The mean (± standard deviation) index percentages of the IgG titers were 74.2 ± 23.6% in the hyperemesis group and 24.3 ± 4.4% in the control group (P< .01, Studentttest).ConclusionInfection withH pylorimay cause hyperemesis gravidarum.