- Background Evidence for a causal relationship between presence of Helicobacter pylori (H. pylori) in gastric mucosa and development of peptic disease is based largely on intervention studies in which eradication of H. pylori led to healing of the lesion. The aim of this study was to assess the importance of H. pylori seropositivity for subsequent development of peptic disease in a prospective study design in young Israelis. Methods A nested case-control serum bank study based on a systematic sample of male and female inductees to the Israel Defense Force. Twenty-nine cases of duodenal ulcer or duodenitis of moderate or higher severity, diagnosed between 1986 and 1995, were individually matched for age, sex, ethnicity, education and year of induction, with five healthy controls each. Presence of anti-H. pylori antibodies in the frozen stored sera was determined by ELISA. Results The geometric mean titre of anti-H. pylori antibodies at baseline was significantly higher in cases (18.3 U/ml) than controls (6.9 U/ml; P = 0.009). The matched odds ratio for peptic ulcer disease by seropositivity was 3.8 (95% CI : 1.4‐10.2). A stronger association was evident for subjects diagnosed >2 years after induction than those diagnosed earlier. The population attributable fraction was 56.6% (95% CI : 15.7‐81.1). Conclusions Pre-existing infection with H. pylori, as determined by seropositivity, is an important determinant of development of duodenal ulcer or duodenitis in young Israelis, supporting the generalizability of an apparent causal association to diverse populations.