How obstetricians' opinions regarding universal screening of pregnant woman for group B streptococcus and their attitude regarding chemoprophylaxis vary from the Centres for Disease Control (CDC) guidelines were studied, and the physician characteristics that predict divergent opinions were determined. Five hundred and eighty-two obstetricians in the Flanders region of Belgium were contacted by a postal survey. Ordinal logistic regression was used to assess obstetricians' characteristics that predict divergence. Only 44% agreed with routine prenatal screening for group B streptococcus of whom 72% would screen at 35 weeks. Intrapartum prophylaxis would be done on the basis of risk factors alone in 38%. Multivariate analysis revealed significant provincial differences (best in Antwerp, worst in West-Flanders) and increasing age was associated with decreasing compliance. It is concluded that a minority of the obstetricians believes in routine prenatal screening and one-third would give prophylaxis on the basis of risk factors alone. Obstetrician's age and province of practice predict divergent opinions.