Retrospective analysis of the case notes of 91 patients attending our combined diabetic/antenatal clinic during 1983-1985 confirmed the reported advantages of pre-conception counselling in established diabetics. 70 of the subjects, however, had glucose intolerance diagnosed during pregnancy and their babies had higher corrected birth weight than established diabetics (3,474 +/- 539 v 3,199 +/- 658 g, p less than 0.025). Caesarian section rates were also increased. Six (9%) babies had congenital abnormalities and their mothers had significantly higher initial HbA1 than the rest, although HbA1 was not a good diagnostic test for glucose intolerance. The management, and even definition, of gestational diabetes is still controversial. Our data suggests that subjects with any degree of glucose intolerance in pregnancy should be managed as carefully as established diabetics and preconception counselling for high risk groups may be beneficial.