Adjustment of the mineralocorticoid activity under substitution therapy is of primary importance in Addison’s disease. We report the clinical and biological conditions of 2 patients with Addison’s disease who developed nephrotic proteinuria during their deficient mineralocorticoid state. Renal biopsy was performed and the specimens processed using conventional histochemistry, Congo red staining, and indirect immunofluorescence. The renal biopsy specimens showed focal segmental glomerular sclerosis and nodular deposits of IgM and C3. Negative for Congo red staining. Serum complement, circulating immune complexes, and anti-DNA and hepatitis B and C and human immunodeficiency virus antibodies were all normal or negative. Absence of vesicoureteral reflux was assessed by X-ray studies. Our observations suggest that deficiency in mineralocorticoid substitution therapy inducing a status of hyperreninemia could play a role in the development of focal segmental glomerulosclerosis in patients with Addison’s disease.