There is a relationship between chronic renal damage and renal function at the time of biopsy. Since the quantification of interstitial lesions with morphometric techniques is very time consuming, a fully automatic method to quantify chronic damage is desirable. Progression of chronic renal damage could be viewed as a texture modification of tubulointerstitial structures. The aim of the present work is to study whether chronic renal damage could be automatically measured by means of texture analysis based on mathematical morphology. Among the morphological tools the best suited for our purpose is that of granulometry. Between four and six fields from 35 renal biopsies with different degrees of renal damage were stained with Sirius red and digitized under polarized light. In each field granulometric function with a circular structuring element was obtained. Interstitial volume fraction was measured with a point counting technique. Glomerular filtration rate at the time of biopsy was available in each case. A positive relationship between granulometric function and glomerular filtration rate was observed (r2 = 0.85). The determination coefficient between interstitial volume fraction and renal function was (r2 = 0.54). In conclusion, we describe a fully automatic method that precisely quantifies interstitial chronic renal damage.