During the period of 1972-1977, 29 patients were treated for primary non-Hodgkin's small intestinal lymphoma (PSIL) in different hospitals in Finland. Most frequently the disease occurred in patients in middle age and there was a male predominance. Clinical symptoms were non-specific. An abdominal mass was felt in 31% of the patients. Radiological findings were mostly non-specific, and often a stricture was revealed. All patients underwent surgery, ten patients curative resection, 15 patients palliative resection and 4 patients exploration and biopsy only. Sixty per cent of the patients who underwent curative resection survived five years compared with ten per cent who underwent palliative resection. The stage of the disease was an important prognostic factor. The five-year survival was 60% for patients with stage I disease, while all the patients with stage IV disease died during the first two years.