The predictive value of gastric metaplasia in the duodenal mucosa in patients Helicobacter pylori-positive patients with duodenal bulb ulcer (DBU) was investigated. One hundred and twenty four randomly selected patients with DBU were included in this prospective study. The detection of Helicobacter pylori (HP) in the stomach and duodenum was carried out with Giemsa (using standard visual analogue scale), rapid urease test (standard Jatrox-HP test, Rohm Pharma, Germany), and polymerase chain reaction (PCR) to detect the specific fragment of ureC HP gene (Helicopol II, Lytech, Russia). Regions of gastric metaplasia of the duodenum were confirmed by periodic acid-Schiff and alcian blue (Serva) staining (pH 1.0; 2.5) Duodenal ulcer (DU) complications were registered within 8 to 10 years. Estimation of the predictive factor (gastric metaplasia in the duodenum) was carried out in patients with non-complicated DU (Group 1; n = 73), and with such complications as bleeding, perforation, penetration, pyloroduodenal stenosis (Group 2; n = 51) which were revealed within the 8 to 10 years of observation. Gastric metaplasia in the duodenum was found in 64 or 87.7% of the 73 patients with non-complicated DU and in 5 or 9.8% of the 51 patients with complicated DU within 8 to 10 years of observation. The following facts about the predictive factor for the prognosis of DU complication were found: the sensitivity of 83.6%, the specificity of 92.8%, the predictive accuracy of 88.7%, the relative risk of the predicted outcome of 7.5, the relative risk of a different outcome of 0.11, the odds ration of 65.4. The study revealed a high and significant (p < 0.001) predictive value of gastric metaplasia in the duodenum as a marker of non-complicated clinical course of DU in HP-positive patients within an 8 to 10-year period.