Primary non-Hodgkin's lymphomas of the stomach are associated with Helicobacter pylori infection. We analyzed gastric lymphoma onset data with respect to prior H. pylori infections based on the multistage theory of carcinogenesis. This theory provides a link between epidemiological data and biological processes. The study involved 133 patients, aged 29–75 years, diagnosed with marginal zone B-cell lymphoma (MZBL) and diffuse large cell B-cell lymphoma (DLBL). A 2-parametric Weibull model was applied to MZBL and DLBL onset data. Median age of diagnosis of MZBL (DLBL) was 59 years (55 years) in males and 65.5 years (64 years) in females. Infection with H. pylori was found in 81.3% (59.5%) of the patients diagnosed with MZBL (DLBL). Lymphoma latency data were fitted to Weibull distributions with a shape parameter of 5.7 for MZBL cases and 4.2 for DLBL. The shape parameter that indicates the number of steps in carcinogenesis was approximately independent of the status of infection with H. pylori in DLBL in contrast to MZBL. It was shown that gastric lymphoma onset data can be described by Weibull distribution functions. The findings support the hypothesis that MZBL and DLBL have different lines of development. There is indication of stronger antigen dependency in the carcinogenesis of MZBL in comparison to DLBL. © 2003 Wiley-Liss, Inc.