BACKGROUND The gastrointestinal tract is the most common site of extranodal involvement in non-Hodgkin's lymphoma (NHL). Primary colorectal NHL comprises 13-18% of all gastrointestinal NHL but is not commonly reported as a separate entity. METHODS This was a retrospective review of the medical records of 19 patients over a 16-year period to evaluate the clinical features and behavior of colorectal NHL. RESULTS A pediatric group of seven male patients presented at an early stage with acute symptomatology. The primary tumor was located in the ileocecum in all cases and intussusception was common. An adult group of 12 patients presented at a later stage with chronic symptomatology. Staging study results were positive by bone marrow biopsy in four of 16 patients (25%), by lymph-angiography in six of 11 patients (54.5%), and by gallium scan in eight of 10 patients (80%). Seven patients relapsed a median of 8 months after treatment. Three other patients died during treatment, one died of other causes, and one died without receiving treatment. The remaining seven patients are alive from 41 to 231 months without evidence of disease. Five of these patients are in the pediatric group, where the median survival was > 72 months. The overall median survival was 45 months. CONCLUSIONS Colorectal NHL is a disease that affects both the pediatric and adult population. Although pediatric patients have an excellent prognosis with anticipated long-term survival after treatment, long-term survival can be expected in approximately 50% of adult patients. In both groups of patients, multimodality therapy with surgery, chemotherapy, and radiation is the treatment of choice.