Burkitt's lymphoma (African lymphoma) was first thought to be limited to tropical and subtropical areas of Africa and New Guinea. The histological criteria described by Wright in 1963 and 1964 made it possible to distinguish the tumour from other forms of malignant lymphoma in children and led to the discovery of a number of undoubted cases of Burkitt's lymphoma in many countries. Retrospective surveys of histological sections have in fact brought to light 65 cases in territories outside tropical Africa. Prior to recognition of the disease as a separate entity, references to probable cases were made in 22 papers from the United States, France, India, and Vietnam. African lymphoma has actually been diagnosed in 23 cases in 10 countries outside Central Africa. The study of fresh imprint preparations, together with new techniques in tissue culture and electron microscopy, will in future render any prospective search for cases of this tumour simpler and more accurate than retrospective studies.