Aims of this study were to investigate the prevalence of metabolic syndrome (MS), diagnosed according to the International Diabetes Federation (IDF) criteria and its relationship with echocardiographic parameters of cardiac structure and function. The study was performed in 707 subjects, age 45-54 years, of the Gubbio Population Study who underwent a comprehensive examination including measurement of body size, blood pressure (BP) and heart rate, 12-lead electrocardiogram, Doppler echocardiography, standardized blood and urine laboratory tests. One hundred and fifty-three subjects were found to have MS, which was more frequent among hypertensive patients than normotensive controls (36.2 vs 13.7%, P<0.001). Apart from visceral obesity present in all subjects by definition according to the IDF criteria, high levels of BP (>130/85 mm Hg) and triglycerides (>or=150 mg/dl) were the most frequently observed components of the syndrome, since their prevalence averaged 75% of those with the syndrome. Left ventricular mass (95.6+/-22 vs 86.4+/-22 g/m(2); P<0.001) and prevalence of left ventricular hypertrophy were increased in the subgroup with MS. Waist circumference, BP and blood glucose were the components of the syndrome with stronger impact on cardiac mass. An early impairment of the diastolic function was detected in this subgroup with a reduction of the early-to-late diastolic filling (0.91+/-0.17 vs 0.99+/-0.23, P<0.001). The results of the present study indicate that MS is frequent in middle-aged general population, particularly in subjects with arterial hypertension. The syndrome is associated to the increase in ventricular mass and the early impairment of diastolic function.