We report seven cases of breast adenocarcinoma and hypertriglyceridaemia associated with the use of tamoxifen. Two cases presented with life-threatening acute pancreatitis. Two cases show a rise in serum triglycerides (TG) after starling tamoxifen. Five patients had some degree of insulin resistance or diabetes which may have aggravated the hypertriglyceridaemia. One additional patient had an apolipoprotein phenotype associated with hypertriglyceridaemia. Fibrates effectively reduced serum TG levels. In general, tamoxifen improves the lipid profile and this may account for the reduction in coronary events in patients taking this drug. However, a rise in serum TG levels has been documented in several studies. Our reports suggest that it is important to screen patients on tamoxifen since hypertriglyceridaemia could cause potentially fatal acute pancreatitis or increase the risk of developing ischaemic heart disease.