After a brief review of the literature concerning scintigraphy of the spleen, its vascular system is described. The presence of numerous anastomoses makes it likely that occlusion of the splenic vein will usually not lead it any parenchymal damage. In five patients with angiographically confirmed spenic vein thrombosis it was shown that radio-colloid scans always demonstrate an enlarged spleen. Poor colloid uptake was thought to be due to a venous reflex mechanism leading to a reduction in the arterial blood supply. The statement found in the literature, that the spleen cannot be shown scintigraphically if the vein is thrombosed, has not been confirmed by us. We tend to the view that the apparent absence of a splenic scan was due to geometric causes.