Patients with FSGS who wish to participate in this study will undergo pre-study evaluation with blood and urine tests. Patients must be on a stable dose of an ACE inhibitor (a drug that lowers blood pressure and reduces proteinuria) for at list 6 months before starting pirfenidone therapy. (Patients who are not already taking an ACE inhibitor will be started on the drug; those who cannot tolerate ACE inhibitors will be given a different drug.) Patients with elevated cholesterol will take a cholesterol-lowering drug. A diet containing approximately 1 gram of protein per kilogram of body weight per day will be recommended.