IGT is a prediabetic state. If IGT can be prevented from progressing to overt diabetes, the hyperglycemia-related complications of this devastating disease can be prevented. Subjects with IGT will be identified with an oral glucose tolerance test (OGTT). Eligible subjects also will have a measurement of first phase insulin secretion and insulin sensitivity using the frequently sampled intravenous glucose tolerance test (FSIVGTT) and carotid intimal media thickness using carotid ultrasound. Following these measurements subjects will be randomized to receive pioglitazone or placebo and they will return every 3 months for determination of fasting plasma glucose (FPG) concentration and interim medical history. Recruitment will take place over 15 months. From the time that the recruitment period ends, subjects will be followed for a total of 24 months on pioglitazone or placebo. The OGTT will be repeated at 15,27, and 39 months, or if the FPG is ≥ 126 mg/dl on the 3-month follow up visits. If the diagnosis of diabetes is established before month 39 or at month 39, the FSIVGTT and carotid ultrasound will be repeated. At 39 months, subjects will be washed out of pioglitazone or placebo and the OGTT, FSIVGTT, and carotid ultrasound will be repeated at month 45.