During the initial phase of the World Health Organization (WHO) "Community Control Program of Hypertension" in Italy, 1190 subjects with high blood pressure derived from a general population random sample (5856 people of both sexes, aged 20 to 64 years) were enrolled in a hypertension register. At the registration visit (RV), each of them gave case history details and underwent a complete clinical examination, blood and urine tests, and a standard 12-lead electrocardiogram (ECG). All the ECGs were read by a single coder, using the second version of the Minnesota Code (MC). We calculated the prevalence of electrocardiographic codes according to sex, age, and the state of antihypertensive treatment. The overall prevalence of electrocardiographic abnormalities (i.e., all codes except 1:0 and isolated 9:4) was 40.8% with a slightly higher prevalence in males than in females: 42.4% versus 39.4%. Codes related to left ventricular hypertrophy (LVH) (3:1 or 3:3) were also more frequent in males (21.2%) than in females (14.5%) but not those related to ischemia (4:1-4:3 or 5:1-5:3). In fact, group 4 codes were present in 4.0% of males and 16.1% of females; group 5 codes, in 5.7% of males and 18.1% of females. Abnormal codes generally increased with increasing age, but those related to LVH did not follow this general rule in males. In fact, in the age class 20-29 years, codes 3:1 were found in 11.1% and codes 3:3 in 17.5% of the subjects, whereas the corresponding frequencies in the oldest age group (60-64 years) were 15.2% and 12.4%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)