Since the original publication of the composite (Matsuda) index for the measurement of insulin sensitivity from plasma glucose and insulin concentrations during the oral glucose tolerance test (OGTT)(1), this index has been widely used by investigators throughout the world. According to Scopus, more than 1,000 articles have cited the original article (1) during the last 10 years, and several modifications of this index have been published (2, 3). Although the basic idea is to use the plasma insulin and glucose areas under the curve (AUCs), the actual time points at which plasma insulin and glucose levels are measured during the OGTT may be few and the time intervals may not be equal. In some studies, fewer time points, usually 0, 60, and 120 min or only 0 and 120 min, have been obtained during the OGTT. We show here that calculation of the composite index using these fewer time points agrees well with the original calculation, which was based on five plasma glucose and insulin measurements. Although it is difficult to imagine a reasonable AUC when samples from only 0 and 120 min are available, the simple index below works quite well.