Background/Rationale. Primary FSGS is a leading cause of end stage renal disease in both children and adults, with complete loss of kidney function in 50% of patients over 10 years. Evidence-based treatment guidelines for FSGS have not been developed because of the lack of controlled studies and the small number of patients included in most reports. Over the past decade, a number of studies have reported therapeutic efficacy for treatment with Cyclosporine-A (CSA) in patients with nephrotic syndrome including patients with steroid resistant FSGS. There have been two controlled trials of treatment with CSA in steroid resistant FSGS, one in children and one in adult patients. Consequently, CSA is the only medication that has been documented to be efficacious in a controlled trial in both children and adults with steroid resistant FSGS. The experience with mycophenolate mofetil (MMF) in the treatment of patients with steroid resistant FSGS has been limited to uncontrolled trials in adult patients and children.