The relationship between a history of hypertension and the quality of its control in routine clinical practice and the risk of acute myocardial infarction was examined in a multicenter, case-control study conducted in Argentina between November 1991 and August 1994, within the framework of the FRICAS study. The cases were 939 patients with acute myocardial infarction and without a history of ischemic heart disease. The controls were 949 subjects identified in the same centers as the cases and admitted with a wide spectrum of acute disorders unrelated to known or suspected risk factors for acute myocardial infarction. The odds ratios and the 95% confidence intervals were derived from multiple logistic regression equations, including terms for age, gender, education, social status, exercise, smoking status, cholesterolemia, history of diabetes, body mass index, and family history of myocardial infarction. The quality of hypertension control was assessed with the most recent blood pressure reading reported by the subjects. Seventy-two percent of hypertensive cases and 62.6% of hypertensive controls had a history of antihypertensive therapy by self-report, when admitted to the medical center. The adjusted odds ratio for acute myocardial infarction due to hypertension was 2.58 (95% confidence interval, 2.08-3.19). The odds ratio was 2.42 (95% confidence interval, 1.88-3.11) when hypertensives reported that their greatest systolic value was below 200 mm Hg (moderate status) and 4.12 (95% confidence interval, 2.87-5.89) when it was above 200 mm Hg (severe status). When the highest diastolic blood pressure value was below 120 mm Hg (moderate status), the risk increased to 2.48 (95% confidence intervals, 1.90-3.24) and to 4.12 (95% confidence interval, 2.83-5.99) when it was above 120 mm Hg (severe status). If the most recent systolic blood pressure was less-than-or-equal140 mm Hg, the odds ratio was 2.59 (95% confidence interval, 1.96-3.41), and it was 3.42 (95% confidence interval, 2.40-4.87) when the value was >140 mm Hg. If the most recent diastolic blood pressure was less-than-or-equal90 mm Hg, the risk increased more than two fold (odds ratio=2.48; 95% confidence interval, 1.91-3.22), and if it was >90 mm Hg, it increased nearly four-fold (odds ratio=3.72; 95% confidence interval, 2.33-5.96). In smokers, the odds ratio was 2.28 in the absence of hypertension and increased to 7.51 when hypertension was present. In this Argentine population, hypertension is a strong and independent risk factor for acute myocardial infarction. In routine clinical practice, the control of blood pressure to levels below 140/90 seems to be required in order to reduce part (but not all) of the risk of acute myocardial infarction in hypertensive patients. (c) 2001 by CHF, Inc.