International, prospective, randomized HOT study aims to determine the optimal BP level under treatment in order to reduce at the most the cardiovascular morbidity/mortality. Defined by randomization, the level to obtain is DBP < or = 80, 85, 90 mmHg. The treatment is started by felodipine 5 mg/day then, if necessary, a bitherapy is prescribed and then, if necessary, a tritherapy. 19,193 patients have been included (BP at randomization 170 +/- 15/105 +/- 4 mmHg). After 1 year treatment, it is possible to search for the influence on the clinical tolerance of sex, age, BP goal, geographic area, time and treatment. The percentage of patients with side effects by BP goals and by treatment type are, during the time and in different geographic areas, the following (NE/Northern Europe = Norway, Switzerland, Belgium, Hungary, Sweden, Denmark, Finland, The Netherlands, UK, Germany, Austria; SE/Southern Europe = Italy, Spain, Greece): [table: see text] The target BP and age don't nearly influence the clinical tolerance. The side effects reported by the physicians are more numerous at the treatment start than at longeur terme. That is due to the therapeutic modifications of the physicians or to a better acceptation of the drugs by the patients or to a real disappearance of the side effects. Reported side effects are more frequent in Southern Europe, France than Northern Europe and more frequent among women that men. The incidence of side effects is proportional to the number of prescribed drugs. Time and the number of antihypertensive drugs appear as the most important factors.