A 91 year old patient presented with constipation, abdominal distension, weakness and anorexia lasting for two days. Computed tomography revealed multiple peritoneal masses with significant growth within days and local invasiveness without regard to anatomical boundaries. No lymphadenopathy or hepatosplenomegaly were found. Abdominal paracentesis showed 60,000 cells/mm3 presumed to be neutrophils. During follow-up, there were no clinical or radiographic signs of peritonitis. Trans-abdominal true-cut biopsy from the peritoneal masses was consistent with diffuse large B cell lymphoma germinal center B cell type, clinically presenting as peritoneal lymphomatosis. FISH cytogenetic study identified single BLC-6 gene in the tumor infiltrating lymphocytes. We speculated that this aberration in the patient's immune system cells contributed to this rare, unusual and aggressive lymphoma presentation in an otherwise non-immune compromised patient.