Characterization of target organ damage from hypertension is of particular interest in African-Americans, and evidence from electrocardiographic studies suggests that left ventricular hypertrophy is a frequent clinical finding of considerable prognostic importance. Echocardiographic studies may permit more precise characterization of the pathologic impact of hypertension on cardiac structure and function. The objective of this study is to characterize left ventricular (LV) structure including measures of wall thickness, septal thickness, internal dimension, and mass in a middle-aged sample of African-Americans using echocardiography. This study is a cohort (cross-sectional) study in which 2445 middle-aged African-American study participants from a population-based sample initially enrolled by the Atherosclerosis Risk in Communities, Jackson, Mississippi Examination Center in 1987-1989 underwent an M-mode echocardiograpic examination at their third or fourth clinic visit in 1993-1996. Measures of LV mass, even where indexed by size were conspicuously greater in men compared to women, and men exhibited a demonstrably steeper gradient of LV mass across the rather restricted age range of the study. However, when gender specific thresholds for LV hypertrophy were utilized, African-American men appear to have lower prevalence of LV hypertrophy than women. The lowest prevalence of LV hypertrophy was observed in African-American men who did not have hypertension (28.4%). The findings confirm previous suggestions from electrocardiographic investigations that cardiac hypertrophy is common, if not epidemic in middle-aged African-American men and women, whether or not they have hypertension.