Helicobacter pylori strains may be either cagA+ or cagA-, and in logitudinal studies, infection with a cagA+ strain has been associated with increased risk for the development of atrophic gastritis and cancer of the distal stomach. We sought to determine the relative proportion of strains producing CagA in different geographic locales, and the extent to which CagA seroprevalence varied in countries with different gastric and esophageal cancer rates. Using an enzyme-linked immunosorbent assay (ELISA) to detect serum IgG to CagA, we examined sera from 468 asymptomatic H. pylori-infected adults from Canada, Peru, China, Thailand, The Netherlands and 3 different ethnic groups in New Zealand. The CagA seroprevalence in Peru and Thailand (82.2% and 78.8%, respectively) were each substantially higher than for the Chinese (37.9%), Canadian (41.9%), Dutch (39.0%) and New Zealand (28.2%) subjects, but within each population, rates were relatively constant across gender and age groups. Reported gastric but not esophageal cancer rates for the 8 studied populations were significantly associated with H. pylori seroprevalence. Variation in CagA positivity rates was not significantly associated with variation in either gastric or esophageal cancer rates. Our data suggest that CagA seroprevalence is not the major factor influencing gastric cancer rates.