A 44-year-old male was evaluated for an iron deficiency anemia. Endoscopic investigation revealed marked serpiginous ulceration of the proximal small intestine due to a B cell lymphoma. Endoscopic small intestinal mucosal biopsies revealed a nodular lymphoid infiltrate, and polymerase chain reaction of biopsy material from the same site demonstrated rearrangement of the bcl-2 gene, the molecular equivalent of the t(14;18) chromosomal translocation. Primary small bowel follicular small cleaved cell lymphoma was diagnosed. Endoscopic tissue biopsies for immunophenotyping, molecular genetic studies or both are a valuable diagnostic aid for precise classification of lymphoid neoplasms in the gastrointestinal tract.