Serum cholesterol, triglyceride, apoprotein Al and B, low-density and hig-density lipoprotein (LDL, HDL) cholesterol levels were quantitated, in two or more consecutive sample collections, in 289 middle aged males to assess the potential for misclassification of dyslipemia, according to the Sociedad Española de Arteriosclerosis and the USA National Cholesterol Education Program guidelines. They were grouped according to serum cholesterol values (less than 5.17 mmol/l, between 5.17 mmol/l and 6.17 mmol/l, and greater than 6.17 mmol/l) and misclassification was arbitrarily identified with different levels of the considered parameters. With cholesterol less than 5.17 mmol/l, misclassification was identified in 18.2% of the subjects, mainly with hypertriglyceridaemia or low HDL-cholesterol values. With cholesterol greater than 6.17 mmol/l there is a clear misclassification although obviated partially by the usual performance of complete routine lipoprotein analysis. Potential for misclassification is more evident when cholesterol was between 5.17 mmol/l and 6.17 mmol/l. To avoid such misclassification, HDL and LDL-cholesterol and serum cholesterol and triglyceride values should be measured in all subjects. Some data on the total cost in a general population screening are also presented; cost that on the author's opinion might be better invested under the control of a centralized institution.