Larger variability of office blood pressure (BP) was reportedly associated with a higher risk of stroke or mortality from all causes. In the present study, we focused on the relationship of variability of office BP and occurrence of acute myocardial infarction (MI). We registered 139 patients receiving antihypertensive therapy for more than 1 year who experienced first-ever episode of MI at the age of 60 years or over. At least two sex- and age-matched (+/- 5 years) control patients were registered for every MI patient. Average systolic and diastolic BP during the 12-month period prior to the occurrence of MI, or the time of registration in the case of control patients, was similar in both patient groups. The office BP variability was evaluated by calculating the variation coefficient (VC) of BP. VC of diastolic BP was significantly higher in the MI patients (10.0 +/- 4.0%) compared with the control patients (8.8 +/- 3.4%). VC of systolic BP was not different between the MI and the control patients. Multiple logistic analysis revealed the relationship of the VC for office diastolic BP to the occurrence of MI was significant after adjustment for BP level, age, gender, body mass index, serum total cholesterol concentrations, diabetes mellitus, and current smoking. In conclusion, larger long-term variability of office diastolic BP during antihypertensive therapy is a predictor of MI.