Pioglitazone is currently used in clinical practice to treat diabetes and this study will examine the potential use of a low dose of the same drug for the treatment of polycystic kidney disease. The purpose of this study is to determine whether the diabetes drug pioglitazone (Actos) is a safe and effective treatment of autosomal dominant polycystic kidney disease when treated in its early stages. Pioglitazone is approved by the FDA for the treatment of diabetes. Pre-clinical models of polycystic kidney disease have shown that low dose treatment with pioglitazone decreases the growth of the cysts. The studies also suggest that effective pioglitazone dosing for polycystic kidney disease may be lower than that used to treat diabetes. The purpose of this study is to see if pioglitazone might slow cyst disease in humans.