BACKGROUND: There are very few cohort studies on the hypertension in family practice. In order to investigate epidemiological characteristics of hypertensive patients and assess the safety and tolerability of newly prescribed antihypertensive monotherapies in Korean patients, a prospective study was carried out. METHODS: A total of 1,181 patients were observed from July 1997 to August 1999. At 2, 4, 8 and 12 weeks after initiation of antihypertensive monotherapy, the patients were evaluated for whether treatment is continued and development of any adverse reactions. RESULTS: Calcium channel blockers(CCBs) were the most commonly prescribed initial drug class (44.2%) in family practice, followed by angiotensin converting enzyme inhibitors(ACEI)(21.0%), angiotensin II receptor antagonists(ARA)(11.8%), beta blockers(9.6%), alpa blockers(3.9%), and diuretics(3.6%). During the first 12 weeks, the percentage of subjects continuing their initial ACEIs(40.7%) was substantially lower than the percentages that of subjects continuing ARAs(66.2%), alpa blockers(63.0%), CCBs(61.3%), beta blockers(55.8%), and diuretics(53.5%), respectively(P<0.01). The following adverse reactions were detected: cough(7.5%), headache(6.1%), dizziness(3.9%), flushing(3.7%) and impotence(2.4%). The incidence of cough associated with ACEI(27.9%) was higher than those of other classes(P<0.01). CONCLUSION: CCBs were the most commonly prescribed initial drug class in family practice, followed by ACEIs, ARAs, beta blockers, alpa blockers, and diuretics. The tolerability of antihypertensive medication was the highest in Korean patients treated with ARAs, followed by CCBs, beta blockers, diuretics, alpa blockers, and ACEIs.