This prospective study was carried out in Dakar, Senegal, to assess the prevalence of Helicobacter pylori infection in symptomatic patients undergoing endoscopy and to evaluate the factors of risk for infection by this type of bacteria in the population. From October to December 1995, 134 patients were included in this study and replied to a standardized questionnaire designed to determine socioeconomic level and living conditions. Diagnosis of Helicobacter pylori infection was based on the combined results of the urea breath test (Clo-test) and histological findings. Helicobacter pylori infection was detected in 82.8% of patients with no significant difference according to sex, age, ethnic group, or living environment (urban or rural). The incidence of infection was also the same in all socioeconomic groups. It was already high in the age group between 11 and 20 years (90.9%). Helicobacter pylori was identified in 76.2% of patients with normal endoscopic findings and in 100% presenting ulcers, erosions, or gastritis. This study shows that the incidence of Helicobacter pylori infection is extremely high regardless of socioeconomic level and that infection begins at a young age. These findings are consistent with the poor hygiene of most people in Senegal.