BACKGROUND: The incidence of primary extranodal non-Hodgkin lymphoma (NHL) of the gastrointestinal (GI) tract has been on the rise.OBJECTIVES: To determine the incidence of primary GI NHL and distribution according to site and histological type in a large North American adult population over a 10-year period.METHODS: All diagnoses of GI NHL made between January 1999 and January 2009 were reviewed using a regional pathology database. Patients ≥18 years of age living within health region boundaries were included. Age- and sex-adjusted incidence rates of GI NHL according to GI site and histological type over a 10-year period were calculated and compared.RESULTS: A total of 149 cases of primary GI NHL were identified during the study period. Age- and sex-adjusted yearly incidence rates ranged from 0.13 per 100,000 in 1999, to 2.39 per 100,000 in 2007. Histological distribution (47% diffuse large B cell lymphoma, 24% extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue type, 8% follicular and 5% mantle cell) and site distribution (47% stomach, 26% small bowel, 17% colon) were obtained with increasing annualized incidence rates for each of these sites over time. Remaining cases included multiple GI sites of involvement (9%) and esophagus (0.7%).DISCUSSION: Population-based GI NHL incidence rates in the present study were higher than those described elsewhere in North America and Europe. Nearly one-half showed high-grade (diffuse large B cell lymphoma) histology at diagnosis. Incidence rates for the colon exceed those described in other studies worldwide.CONCLUSION: Because the majority of GI NHL are diagnosed on endoscopic biopsy, clinicians and pathologists must be vigilant of this entity.