The aim was to determine the prevalence of small bowel involvement in patients with gastrointestinal (GI) lymphoma by double-balloon endoscopy (DBE). We examined 29 patients with primary GI lymphoma by oral and anal DBEs. Clinicopathologic features related to the prevalence of diminutive small bowel involvement and the clinical outcome were retrospectively investigated. Diminutive small bowel lesions were found in 14 patients. The prevalence of the lesions was not different between patients with primary small bowel lymphoma and those with primary extra-small bowel lymphoma (50% versus 47%, P = 0.6). However, clinical stage was more advanced in patients with the lesions than in those without (P < 0.05). The lesions were more frequently found in T-cell lymphoma (100%) and follicular lymphoma (77%) than in the other types of lymphoma (15%) (P < 0.05). Diminutive small intestinal lesions occur in patients with GI lymphoma, especially in those with follicular lymphoma and T-cell lymphoma. GI lymphomas of these histologic types are candidates for scrutiny by DBE.