Objective: Autopsy/cadaver data indicate that many organs and tissues are smaller in the elderly compared to young adults, however, in-vivo data are lacking. The aim of this study was to determine whether the mass of specific high metabolic rate organs are different with increasing age using magnetic resonance imaging. Method: 75 healthy women (41 African-Americans and 34 Caucasians, age range 19-88 years) and 36 men (8 African-Americans and 28 Caucasians, age range 19-84 years) were studied. Magnetic resonance imaging (MRI) derived in vivo measures of brain, heart, kidneys, liver, spleen, were acquired. Left ventricular mass (LVM) was measured by either echocardiography or cardiac gated MRI. Total body fat mass and fat free mass (FFM) were measured with a whole-body dual-energy X-ray absorptiometry (DXA) scanner. Multiple regression analysis was used to investigate the association between the organ mass and age after adjustment for weight and height (or DXA measures of FFM), race, sex and interactions among these variable. Result: No statistically significant interaction was found among age, sex and race in any regression model. Significant negative relationships between organ mass and age were found for brain (p<0.0001), kidneys (p=0.01), liver (p=0.001) and spleen (p<0.0001). A positive relationship between LVM and age was found after adjustment for FFM (p=0.037). Conclusion: These findings demonstrate that age has a significant effect on brain, kidneys, liver, spleen and heart mass. The age effect was independent of race and sex.