The prevalence, prognosis, and predictors of left ventricular hypertrophy (LVH) are reviewed, and theories of the pathogenesis of the relation between LVH and poor prognosis are summarized to highlight controversies in the field. In the Framingham Heart Study, which consists largely of white people, echocardiographic LVH has a prevalence of 14% in men and 18% in women. The prevalence of LVH is reported to be elevated in African Americans compared with whites, although the higher prevalence has been attributed to the increased prevalence of hypertension and obesity. Echocardiographic LVH is independently associated with a variety of cardiovascular endpoints, including coronary heart disease and stroke. Furthermore, after adjusting for other cardiovascular disease risk factors, LVH is associated with a doubling in mortality in both white and African American cohorts. Despite the intensive investigation of LVH, there remain many unanswered questions: To what extent do genetic or other factors account for the large portion of the variance in LVH that remains unexplained? What is the prognosis of LVH and left ventricular geometry in a population-based African American cohort? How does the development and progression of LVH relate to other risk factors and their treatment? What is the relation of LVH to poor prognosis? The proposed Jackson Heart Study will help address many important unanswered questions regarding LVH.