Helicobacter pylori is now regarded as a major gastroduodenal pathogen that is etiologically linked with duodenal and gastric disease. It has been suggested recently as an important factor for nongastroenterologic conditions such as coronary heart disease and diabetes mellitus. In this study, we planned to investigate the prevalence of H. pylori in diabetic patients and to evaluate five different diagnostic tests. Group I consisted of 67 patients with type II diabetes mellitus and seventy-three aged-matched health people served as control in group II. Group I was divided in two subgroups with good (Group IA) and poor (Group IB) glycemic control. H. pylori was diagnosed by five different tests: 1) biopsy, 2) culture, 3) gram staining, 4) imprint cytology and 5) brushing cytology. The usefulness of each test for each group was statistically compared. There was a higher prevalence for H. pylori in diabetic patients. This study showed that two positive out of five tests was most reliable for predicting the H. pylori in diabetic and nondiabetic patients. In conclusion, the prevalence of H. pylori is high in diabetic patients. Peristaltic activity, and impaired nonspecific immunity must be evaluated as risk factors in diabetics. We recommend that the 'gold standard' should be regarded as two positive out of these five different tests.