A high prevalence of upper gastrointestinal symptoms is described in diabetic patients and, at least in part, this has been attributed to abnormal emptying of the stomach. In an unselected small series of dyspeptic patients with Type 2 diabetes mellitus (DM2), we previously described a. higher prevalence of Helicobacter pylori (Hp) infection associated with autonomic neuropathy (AN) than in non-diabetic subjects. To evaluate the prevalence of Hp and its relationship with AN, we studied 164 DM2 patients, matched for sex, age (+/- 5 years) and body weight (+/- kg) to 164 non-diabetic subjects, all affected with dyspepsia of unknown origin. Results document that the prevalence of peptic ulcer is similar in both groups of patients (20.1 vs 29.3%, P = n.s.); chronic gastritis was 50% in the control group and 35.4% in the DN2 group (P < 0.01) and dyspepsia without ulcer and gastritis (simple dyspepsia) was significantly more frequent in DM2 patients than in non-diabetics (44.5 vs 20.7%, P < 0.01). Hp infection was documented by histology of gastrointestinal mucosa in 74.4% of the DM2 patients and in 50% of the controls (P < 0.01) (ulcer: 97 vs 71%, P < 0.05; gastritis: 72 vs 43.5%, P < 0.05; simple dyspepsia: 66 vs 35%, P < 0.01, respectively). Autonomic neuropathy was found in 65.2% of the DM2 patients (90.9% of patients with ulcer, 65.5% with gastritis and 53.4% with simple dyspepsia). A significant concordance (84.7%, P < 0.001) was found between the presence of AN and Hp infection. Data provide, for the first time, direct evidence for a higher frequency of Hp infection in dyspeptic patients affected with DM2 than in non-diabetic subjects. In addition, in diabetic patients the frequency of non-ulcer, non-gastritis dyspepsia is two times higher than in non-diabetics and is strictly associated with autonomic neuropathy, acting as a favoring factor for occurrence and recurrence of gastrointestinal disease. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.