Great advances have been made in the management of diabetes during the past decade. Whereas only one class of oral medications (the sulfonylureas) was available for the treatment of type 2 diabetes in the early 1990s, we now have five classes of oral antidiabetic agents from which to choose. The thiazolidinedione class of medications was first introduced to the United States when troglitazone was marketed during early 1997. Rosiglitazone, approved by the FDA during the spring of 1999, was the second thiazolidinedione to be marketed in the United States. Similar to troglitazone, rosiglitazone improves insulin sensitivity in patients with type 2 diabetes by activating peroxisome proliferator-activated receptor-gamma (PPARgamma) receptors in adipose tissues, skeletal muscles, and the liver. The efficacy and safety of rosiglitazone therapy in patients with type 2 diabetes have been demonstrated in a number of clinical studies, which are summarized in this article. Selected characteristics of rosiglitazone are compared with those of pioglitazone--the other thiazolidinedione currently available in the United States. Edema of mild to moderate severity has been reported in approximately 5% of patients treated with rosiglitazone during clinical trials. Therefore, caution must be taken when this agent is administered to patients with heart failure. Rosiglitazone has also been associated with elevations of total, LDL, and HDL cholesterol during clinical trials. However, the LDL:HDL cholesterol ratio or the total:HDL cholesterol ratio has mostly been observed to be unchanged. Although liver toxicity has not been observed with rosiglitazone during clinical trials, the safety of this drug for long-term usage and in larger patient populations remains to be established in further clinical studies and in postmarketing experience.