A new cause of chronic interstitial fibrosis of the kidney, recently identified in Belgium, was found to be related to a slimming regimen that included Chinese herbs. Thirty-three biopsy-proven cases of this nephropathy are discussed, with special reference to the pathologic aspects. Extensive interstitial fibrosis with atrophy and loss of the tubules was the major lesion; it was predominantly located in the superficial cortex. The glomeruli were relatively spared. They nevertheless showed a mild collapse of the capillaries and wrinkling of the basement membrane. Thickening of Bowman's capsule was the rule. Interlobular and afferent arterioles showed thickening of their walls due to swelling of the endothelial cells. These aspects suggest that the primary lesions could be located in the vessel walls, leading to ischemia and interstitial fibrosis. On the other hand, they are characteristic enough to allow the pathologist to suspect the diagnosis even in the absence of an anamnesis of ingestion of Chinese herbs.