Objective:To compare cognitive, language, and motor skills and results of neurological examination in 2-year-old children born to mothers with gestational diabetes mellitus treated with metformin with those treated with insulin.Method:The children of mothers with gestational diabetes mellitus randomized to metformin (n = 75) or insulin (n = 71) treatment during pregnancy were examined by standardized developmental and neurological measures; the Bayley Scales of Infant and Toddler Development (Bayley-III) and the Hammersmith Infant Neurological Examination.Results:There were no significant differences between the metformin and insulin groups in the Bayley Scales of Infant and Toddler Development (Bayley-III) test of cognitive scale (p = .12), receptive communication (p = .14) or expressive communication (p = .75), fine motor scale (p = .10) or gross motor scale (p = .13), or the global scores of Hammersmith Infant Neurological Examination (p = .14). None of the children had a clinically significant developmental problem. However, compared with age-adjusted norms, a trend for weaker language performance was observed in both study groups.Conclusion:No differences in neurodevelopmental outcome were seen in 2-year-old children born to mothers with gestational diabetes mellitus (GDM) treated with insulin or metformin during pregnancy. The results suggest that children born to mothers with GDM and exposed to metformin in utero do not systematically need extensive formal neurodevelopmental assessment in early childhood.