The incidence of district (cardiac, cerebral, renal) and systemic vascular complications was studied in a population of 3992 hypertensive in-patients during the period from 1984 to 1988. The total number of male hypertensive patients was always higher (2355) than that of female hypertensive patients (1637). From the analysis of results it appears that 11.01% of male hypertensive patients and 15.85% of female hypertensive patients were diagnosed as being affected by uncomplicated essential arterial hypertension, whereas 88.97% of male and 84.12% of female hypertensive patients suffered from arterial hypertension with varying percentages of cardiac, cerebral, renal or systemic-type atheroarteriosclerotic complications. The prevalence of the male sex was particularly evident in the case of cardiac complications. Given the peak incidence of the various types of complications when analysed by decade of age, an earlier incidence of cardiac and renal complications was found in male hypertensive patients which anticipates the complications found in female hypertensive patients by approximately one decade. Lastly, the paper underlines the social importance of essential arterial hypertension and the need to develop efficacious primary and secondary prevention in order to reduce the incidence of complications which today represent the most severe aspect of hypertension.