The severity and incidence of asthma have increased drastically in the developed nations of the world over the last decades. Currently, some evidences indicate an inverse association between Helicobacter pylori and asthma, but some studies did not get the same conclusion. To make this question clear, we systematically reviewed the published evidence for an association between H. pylori infection and asthma. Medline and SCI databases up to April 2012 were searched to identify studies that evaluated the association between H. pylori and asthma. Relevant publications were searched using the following keywords or synonyms: asthma or Helicobacter pylori. Methodologic quality was scored by using a standardized list of criteria, and meta-analysis was conducted to calculate crude odds ratios (ORs) with 95% confidence intervals (CIs). Nineteen studies met our inclusion criteria: nine cross-sectional studies, seven case-control studies, and three prospective cohort studies. The overall methodologic quality score was high. Pooled ORs for the association between asthma and H. pylori infection were 0.84 (95% CI: 0.74-0.96) in nine cross-sectional studies, 0.94 (95% CI: 0.79-1.12) in seven case-control studies, and 0.82 (95% CI: 0.53-1.27) in three cohort studies. The pooled OR for all included studies was 0.81 (95% CI: 0.72-0.91) in children and 0.88 (95% CI: 0.71-1.08) in adults. We found a weak evidence for an inverse association between asthma and H. pylori infection both in children and in adults. © 2012 Blackwell Publishing Ltd.