To study cost-effective screening criteria for gestational diabetes, a prospective study of 1012 patients was completed. All patients underwent a glucose screen between 26 and 30 weeks of gestation, consisting of a 50-g oral glucose load followed by a one-hour plasma glucose determination. Patients with a glucose screen greater than or equal to 130 mg/dL were studied with a standard three-hour oral glucose tolerance test. The incidence of gestational diabetes was 2.4% (24 of 1012). Only one gestational diabetic was identified with a glucose screen below 150 mg/dL. Twenty-two of the 24 cases were at least 24 years old. Twenty-one of the 24 (88%) gestational diabetes had a glucose screen greater than or equal to 150 mg/dL and were 24 years old or greater. The cost of the diagnosis in these latter patients was 40% of the cost of diagnosis of universal screening with a threshold of 130 mg/dL. It is concluded that screening with a threshold of 150 mg/dL only patients who are at least 24 years old should be considered an alternative to universal screening.