The aim of this study was to investigate whether there was a relationship between H. pylori (Helicobacter pylori) infection positivity and characteristics (time and duration) of hyperemesis gravidarum (HG) symptoms. Forty-seven pregnant women with HG and 39 pregnant controls at the same gestational weeks without any gastrointestinal symptoms were included in this prospective study. H. pylori serum Immunoglobulin (Ig) G concentrations were determined by enzyme-linked immunoadsorbent assay (ELISA) in patients with HG and controls. Positive serology for H. pylori was correlated with the duration of symptoms in patients with HG. The prevalence of H. pylori infection was 85.1% (40 of 47) and 64.1% (25 of 39) in patients with HG and controls, respectively (p <0.05, chi (2) test). Mean values of H. pylori IgG (+/- standard deviation) were significantly higher in patients with HG than in controls (22.66 aIU/mL +/- 22.34 vs. 11.54 aIU/mL +/- 13.89, p <0.01, Student's t-test). In HG group, time (gestational weeks) and the duration (weeks) of HG symptoms for patients serologically positive and negative for H. pylori were 6.95 +/- 1.55 versus 6.58 +/- 1.78 weeks, (p >0.05, Student's t-test) and 8.35 +/- 5.28 versus 11.40 +/- 7.17 weeks (p >0.05, Mann-Whitney U-test), respectively. There was no correlation between duration of HG symptoms and serum H. pylori IgG concentrations. Although a majority of pregnant women with HG were serologically positive for H. pylori infection, there was no correlation between positive serology and duration of symptoms, which is not suggestive of a direct causal relationship between H. pylori infection and HG.