Background:  There are also reports from other parts of the world indicating the presence of significant association of H. pylori infection and hyperemesis gravidarum, a bothersome condition that affects pregnant women.  Objective: To test the hypothesis that whether H. pylori infection is associated with hyperemesis gravidarum among Iranian H.P carriers. Methods: From November 1999 to February 2001, we enrolled 54 pregnant women with hyperemesis gravidarum and 53 asymptomatic pregnant women (control group) in a prospective study.  Using a specific serum IgG against H. pylori, the seroprevalence of H. pylori infection was determined in both study and control groups. Results: Serologically positive H. pylori infection was detected in 44 (82%) out of 54 patients with hyperemesis gravidarum and 29 (55%) out of 53 asymptomatic pregnant women. The prevalence was significantly (p<0.01) higher in those with hyperemesis gravidarum than those in the control group.  The mean±SD of the IgG titer in the study group (69.7±77.5) was significantly (p<0.01) more than that of the control group (34.5±47.8). Conclusion: H. pylori infection may cause hyperemesis gravidarum.