The National Seroepidemiologic survey was carried out by the General Directorate of Epidemiology of the Ministry of Health from March 1987 to May 1988. One of the objectives of this survey was to know the mean cholesterol levels in the whole country and in each of the different states of the Mexican Republic by sex and in the different age groups. Of the 68,257 individuals studied, 39,990 (58.6%) were females and 28,267 (41.1%) males. The blood samples were processed at the Lipid Laboratory in the Endocrinology Department of the National Institute of Cardiology "Ignacio Chávez". The mean serum cholesterol levels were for the entire country 184 and 185 mg/dl in adult males and females, respectively, and 145 in males and 149 mg/dl in females in the age group below 20 years old. The northern states and two states in the southeast (Yucatan and Campeche) had the highest mean values of the country, and were found to be very similar to those observed in the United States population. When the values seen during childhood were compared with those attained on adult age, an increment of around 33 percent in the mean cholesterol levels was disclosed. This finding was similar in the different regions of Mexico as well as in the USA population. Also, the states with the highest mean cholesterol values in the young population had the highest values during adulthood (R2 = 0.90 and 0.91, for males and females). This information can be of great value for developing public health strategies to diminish the incidence of coronary heart disease.