Sand rats fed a hypercaloric diet manifest obesity and diabetes. We have used this model to develop hypercholesterolaemia and describe the beneficial action of Olea europea var. oleaster leaves. Twenty-eight sand rats submitted to a high cholesterol diet for four months were assigned to control and treated groups. Plant decoction at 10 per cent was given orally for two months. Results showed that the control group exhibited hyperglycaemia, glucose intolerance, hypercholesterolaemia and moderate hyperinsulinaemia. Light microscopic study showed thickening of capillary walls in skin, pancreas and kidney. The treatment produced hypoglycaemic (43 per cent, p < 0.001), antihyperglycaemic (48 per cent, p < 0.001) and hypoinsulinaemic (39 per cent, p < 0.01) activities. In addition, the plant presented a hypocholesterolaemic effect (47 per cent, p < 0.001) accompanied by lowering of oxidized LDL (30 per cent, p < 0.01). Accordingly, capillary wall thickening was reduced in skin and pancreas and completely prevented in kidney. The data demonstrate that oleaster leaves possess at least two active compounds to treat hypercholesterolaemia and diabetes.