We have compared the characteristics of those screened and unscreened for gestational diabetes mellitus (GDM) in a multiethnic population in New Zealand. All obstetric records for a 12-month period were reviewed manually and electronically. Pre-gestational diabetes status, screening for GDM and obstetric history were recorded. Data for 4885 singleton pregnancies, uncomplicated by known pre-existing diabetes were available. Overall 50.6% of women were screened for GDM using a glucose challenge test, ranging between 36.8% among Europeans to 68.5% among Pacific Islanders (P<0. 001). Attendance at a follow up oral glucose tolerance test among those with a positive screen was 77.4%, with no ethnic difference. Rates of GDM were 3.3, 7.9 and 8.1% for Europeans, Maori and Pacific Islanders. An estimated 45-72% of women with GDM went undetected. Although increasing weight was associated with an increased likelihood of screening, 44.9, 34.8 and 21.1% of obese (weight 85+kg) Europeans, Maori and Pacific Islanders, respectively, were not screened. Increasing age was not associated with increased screening. Screening for GDM is not occurring even in those with clear and agreed indications for selective screening. We hypothesise that the current debate over criteria for selective screening may be undermining screening for those most at risk.