The predictive value of changes in the severity of electrocardiographic left ventricular hypertrophy (ECG-LVH) during antihypertensive therapy remains unclear in isolated systolic hypertension (ISH). In a Losartan Intervention For Endpoint reduction in hypertension substudy, we included 1320 patients aged 54-83 years with systolic blood pressure (BP) of 160-200 mm Hg, diastolic BP <90 mm Hg and ECG-LVH by Cornell voltage-duration product and/or Sokolow-Lyon voltage criteria, randomized to losartan- or atenolol-based treatment with a mean follow-up of 4.8 years. The composite end point of cardiovascular death, non-fatal myocardial infarction (MI) or stroke occurred in 179 (13.6%) patients. In Cox regression models controlling for treatment, Framingham risk score, as well as baseline and in-treatment BP, less severe in-treatment ECG-LVH by Cornell product and Sokolow-Lyon voltage was associated with 17 and 25% risk reduction for the composite end point (adjusted hazard ratio (HR) 0.83, 95% confidence interval (95% CI:) 0.75-0.92, P=0.001 per 1050 mm × ms (1 s.d.) lower Cornell product; and HR 0.75, 95% CI: 0.65-0.87, P<0.001 per 10.5 mm (1 s.d.) lower Sokolow-Lyon voltage). In parallel analyses, lower Cornell product and Sokolow-Lyon voltage were associated with lower risks of cardiovascular mortality and MI, and lower Sokolow-Lyon voltage with lower risk of stroke. Lower Cornell product and Sokolow-Lyon voltage during antihypertensive therapy are associated with lower likelihoods of cardiovascular events in patients with ISH.