To assess the prevalence of Helicobacter pylori in diabetes mellitus, a serological test used to detect antibodies to H. Pylori in patients with diabetes mellitus. Within six months, 45 insulin-dependent, 98 non-insulin-dependent, and a control group of 159 outpatients were enrolled in this study. The age adjusted seroprevalence rate of Helicobacter pylori were determined using a commercial anti-Helicobacter pylori IgC and IgA ELISA (Bio-Rad). The prevalence rates increased with age in all age groups until 60-70 years. In diabetic patients, the frequency of Helicobacter pylori infection was higher than control subjects in nearly all age groups, reaching significance in three age categories of NIDDM patients and in one age category in IDDM patients. This higher seroprevalence could not be explained by differences in socioeconomic status or use of antibiotics.