Objectives: To establish a relationship between hyperemesis gravidarum (HG) and Helicobacter pylori (H. Pylori) infection by histologic testing. Methods: Twenty patients with severe HG (Group I) and 10 volunteer pregnant women without gastric complaints (Group II) were included in the study. Endoscopic evaluations were done in both groups and biopsies were obtained from the antrum and corpus for the histopathologic diagnosis of H. pylori. The groups were compared with the chi(2)-test and Fisher's exact test where appropriate. Results: H. pylori was diagnosed in 19 (95%) of 20 patients in Group I and 5 (50%) of 10 patients in group II. H. pylori densities in the antrum and corpus were higher in Group I and the differences between the two groups were statistically significant. The biopsy specimens revealed significant inflammation and H. pylori activation processes in patients with HG, and in 18 of 19 patients inflammation scores were greater than + 2 on the scale. Pangastritis was demonstrated by endoscopic examination in 17 of 20 patients with HG. Enterogastric reflux was also diagnosed in 10 patients. In the control group, three patients had antral gastritis. Conclusions: We suggest that in patients with intractable nausea and vomiting during pregnancy, pangastritis and enterogastric reflux are the main endoscopic findings and that these findings are closely associated with H. pylori infection, which can be diagnosed histologically. The degree of gastric complaints may be associated with the density of H. pylori infection. (C) 2002 International Federation of Gynecology and Obstetrics. Published by Elsevier Science Ireland Ltd. All rights reserved.