Flavonoids have been suggested to be responsible for the potential beneficial properties of fruit and vegetables on stomach cancer risk. To provide further information on flavonoids, proanthocyanidins, and gastric cancer risk, we analyzed data from a case-control study conducted in Italy. Subjects were 230 cases with incident, histologically confirmed gastric cancer and 547 frequency-matched controls, admitted to the same hospitals of cases for acute, non-neoplastic conditions. Subjects were interviewed using a reproducible and valid food frequency questionnaire. We estimated the odds ratios (ORs) of gastric cancer and their corresponding 95% confidence intervals (CIs) using unconditional logistic regression models including terms for major recognized gastric cancer risk factors. The ORs of the highest quintile of intake compared to the lowest were below unity for all classes of flavonoids, in the absence, however, of significant associations. Strong inverse relations were found for proanthocyanidins. The OR was 0.44 (95% CI, 0.25-0.76) for monomers and dimers combined and 0.36 (95% CI, 0.21-0.63) for polymers with three or more mers. Further adjustment for fruit and vegetables, or vitamin C, did not materially change these associations. This is the first epidemiological study to suggest that dietary proanthocyanidins have a favorable role on gastric cancer risk.