The diagnosis of gestational diabetes requires that two of the four 100 gm, 3-hour oral glucose tolerance test values be elevated. Our report evaluates the usefulness of repeating the oral glucose tolerance test in patients who have only one abnormal value. One hundred six patients who had abnormal results of diabetes screening tests (glucose level greater than or equal to 130 mg/dl) and whose glucose tolerance test had one abnormal value underwent repeat glucose tolerance testing at an average of 4.6 weeks later. Thirty-six patients (34%) had two abnormal values on the repeat test and were classified as having gestational diabetes. Our results indicate that the finding of one abnormal value on a glucose tolerance test denotes a significant risk for the development of gestational diabetes.