Obesity is a risk marker for progressive renal function loss in patients with known renal disease. There is, however, increasing evidence that obesity may also damage the kidney in otherwise healthy subjects. There appears to be an intriguing parallel between the renal effects of obesity and those of diabetes. First, an increased renal blood flow and glomerular filtration rate has been described in obesity and, second, microalbuminuria is found to be related to obesity. These two events are known to predict future loss of renal function in diabetes. The mechanism responsible for the renal damage in obesity has not been established but there is evidence suggesting that this might be related to both hormonal changes as well as low-grade inflammation.