OBJECTIVES: To investigate rates of 'any' and 'predominant' breastfeeding in hospital among Indigenous and non-Indigenous women with and without gestational diabetes mellitus (GDM). METHODS: A retrospective study of singleton infants born from July 2007 to December 2010 at Cairns Hospital, Australia, following GDM pregnancy, using linked hospital and birth data (n=617 infants), with a subsample of medical record reviews (n=365 infants). Aggregate data were used to compare to breastfeeding rates among infants born following non-GDM pregnancy (n=7,894 infants). RESULTS: More than 90% of all women reported any breastfeeding before hospital discharge. About 80% of women without GDM reported predominant breastfeeding. Despite significant increases over time (p<0.0001), women with GDM were less likely to predominantly breastfeed (OR 0.32, 95%CI 0.27-0.38, p<0.0001); with lower rates among Indigenous women (53%) compared with non-Indigenous (60%) women (OR 0.78, 0.70-0.88, p<0.0001); and women having a caesarean birth or pre-term infant. CONCLUSIONS: Rates of predominant in-hospital breastfeeding were lower among women with GDM, particularly among Indigenous women and women having a caesarean or pre-term birth. IMPLICATIONS: Strategies are needed to support predominant in-hospital breastfeeding among women with GDM. © 2017 The Authors.