BACKGROUND: Information on exclusive breastfeeding (BF) and BF initiation following bariatric surgery (BS) among obese women with diabetes mellitus (DM) and without DM (non-DM) is limited. METHODS: Retrospective cohort study. Obesity was defined by BMI (kg/m2) as grade 1 (30–34.9), grade 2 (35–39.9) or grade 3 (≥40). The 65 women in the DM group (40 women with gestational, 19 with Type 2 and 6 with Type 1) was similar to 84 with non-DM in BS type: Roux-en-Y (51 vs 55%), sleeve gastrectomy (32 vs 35%), laparoscopic gastric banding (17 vs 7%) and gastro-duodenal anastomosis (0 vs 4%). RESULTS: Women with DM were older (35 vs 33y), of advanced age (54 vs 27%), with higher prevalence of grade 3 obesity (66 vs 46%), chronic hypertension (31 vs 10%), delivery of late-preterm infants (23 vs 10%) and neonatal hypoglycemia (25 vs 12%). Although infant feeding intention was similar: BF (66 vs 79%), partial BF (9 vs 7%) or formula (25 vs 14%), at discharge women with DM had lower exclusive BF (29 vs 41%) and BF initiation rates (68 vs 76%) than those with non-DM. Women with grade 3 obesity (52% were DM) differed from those with grades 1-2 (34% were DM) in exclusive BF (27 vs 52%), and BF initiation rates (66 vs 86%). CONCLUSION: After BS, women with DM, especially those with grade 3 obesity, had higher rates of chronic hypertension and preeclampsia and lower rates of exclusive BF and BF initiation than those who had DM but had less severe obesity.