The criteria for the diagnosis and management of diabetes in pregnancy are currently based upon maternal, neonatal, and obstetric outcomes. We have investigated the long-term impact of antenatal insulin therapy on adiposity of the offspring. A cohort of offspring from 20/35 women with past gestational diabetes, who had been biochemically and anthropometrically characterized at birth, were followed up after 2 years 8 months (standard deviation 1 month). Measures of growth and adiposity were taken. In comparison with offspring of women treated with diet alone, offspring of women treated with insulin therapy had less subscapular fat (median (interquartile range): 7.9 (7.0-9.4) vs 5.9 (5.4-7.9) mm) and less biceps fat (6.3 (6.0-9.0) vs 5.1 (4.3-6.6) mm). This was in spite of the insulin-treated mothers being more obese, older, and more hyperglycaemic than those who received diet alone. In conclusion, insulin therapy in gestational diabetes may reduce the incidence of obesity in the offspring of women with gestational diabetes and this should now be tested by a larger, randomized controlled trial.