Medullary nephrocalcinosis is a rare condition typically observed in metabolic conditions prone to renal calcium stones. Randall's plaques are very frequently observed in the common idiopathic calcium-oxalate nephrolithiasis. These plaques are apatite mineral structures, and we propose they also are an example of nephrocalcinosis. While these calcium deposits are generally considered to be the consequence of purely physico-chemical phenomena, we advance the hypothesis that they form because of a true ectopic biomineralization in the renal tissue. Henle's loop epithelial cells, or pericyte-like interstitial cells, or papillary stem-cells differentiating along a bone lineage could be involved.