Echocardiographic left ventricular (LV) wall thickness increases with age, suggesting LV hypertrophy. However, autopsy studies have shown no change, or even a decrease, in LV mass with age. With many pathologies, LV remodeling results in changes in ventricular shape. Age-associated LV shape change might explain this discrepancy, although this has not been studied. Magnetic resonance imaging (MRI) was used in 336 healthy, normotensive adults (mean age 56 ± 18 years; 200 women, 136 men) to measure LV mass, end-diastolic LV wall thickness, length, diameter, and shape. Echocardiographic LV mass was measured in a subset of 86 subjects by a standard algorithm. In women, LV wall thickness increased by 14% (r = 0.19, p <0.02), whereas LV length decreased by 9% (r = −0.26, p = 0.0006); LV diameter was unchanged. Thus, LV mass did not vary with age (r −0.04, p = 0.06) and the sphericity index decreased (r = −0.165, p <0.05). In men, LV wall thickness and diameter were unrelated to age, but there was an 11% decrease in LV length (r = −0.29, p = 0.003); therefore, there was an 11% decrease in LV mass (r = −0.20, p = 0.019) and a decrease in the sphericity index (r = −0.218, p <0.04). No change occurred in echocardiographic LV mass with age in either gender, although echocardiographic LV wall thickness increased in both. The left ventricle becomes more spherical with age in normal adults due to reduced LV length. In women, increased LV wall thickness offsets the decreasing LV length, whereas in men, LV wall thickness fails to compensate, resulting in decreased LV mass with age.