Three thousand seven hundred and eighty-three patients with non-malignant hypertension attending the Glasgow Blood Pressure Clinic between 1968 and 1983 were followed prospectively for an average of 6.5 years. Left ventricular hypertrophy (LVH) was present at the outset in 34.5% of the men, and 12.8% had ST-T changes. The corresponding figures for women were 21.5% and 8.8%. The prevalence of LVH increased with the severity of hypertension and was higher for a given blood pressure level in men than in women. All-cause age-adjusted mortality, expressed as deaths per 1000 patient-years, was 27.6 for men with normal electrocardiographs, 43.2 for men with LVH only (P less than 0.001) and 56.9 for men with LVH and ST-T changes (P less than 0.001). Similar trends were seen in women. The excess risk associated with LVH, with or without ST-T changes, could not be explained by age, increased blood pressure at referral to the clinic, or smoking habit, when these factors were considered either separately or in combination (regression analysis). Thus, our study demonstrates that LVH, with or without ST-T changes is an independent risk factor for mortality in hypertensive patients.