The antihypertensive treatment with a single agent is not useful for the arterial pressure control in a significant number of patients. In such cases, combined treatment or drug substitution are recommended (sequential or substitutive monotherapy). In the last years, the fixed dose combinations in one single pharmaceutical preparation have proliferated. These associations must fulfill a number of conditions in order to be considered rational, as for instance the compatibility of its pharmacokinetic features, properly dosing, the absence of new secondary effects and the high efficiency showed in most of patients. The advantages of these combinations are the comfort and easiness of the therapeutic schema, antihypertensive action strengthening, less secondary effects when dose is reduced, and perhaps a synergism in the protection of target organs. The most popular combinations are: potassium sparing diuretic plus thiazide, diuretic plus beta block, diuretic plus ACEI, or calcium antagonist plus ACEI.