This prospective investigation was undertaken to compare the value of routine versus selective diabetes screening in a group of predominantly middle-class, healthy, Caucasian pregnant women. Two thousand consecutively chosen persons were divided into two groups: those to undergo routine screening between 24 and 28 weeks' gestation and those to be tested selectively in the presence of standard risk factors. The two groups of patients were otherwise similar. The method of screening involved a 50 gm oral glucose challenge, followed by a 3-hour glucose test if necessary. The incidence of gestational onset diabetes in the selectively screened group (19/453, 4.2%) was twice that in the routinely screened group (21/1000, 2.1%). Evidence of glucose intolerance without a risk factor was found in only one case (1/1000, 0.1%) in the routinely screened group. This assessment of our clinical practice has allowed us to safely eliminate the need for diabetes screening in more than half of our private patients, which will reduce office time, patient inconvenience, and expense.