BACKGROUND: For individuals with obesity and type 2 diabetes, weight loss improves insulin sensitivity and β-cell function and can induce remission of diabetes. However, the long-term comparative effectiveness of standard gastric bypass and sleeve gastrectomy on remission of type 2 diabetes remains unclear. We aimed to compare the effects of gastric bypass and sleeve gastrectomy on type 2 diabetes remission, weight loss, and cardiovascular risk factors 5 years after surgery. METHODS: We present a secondary analysis of a two-armed, single-centre, triple-blind, randomised controlled trial conducted at a public tertiary obesity centre in Norway. Adults (ie, age ≥18 years) with type 2 diabetes and obesity were randomly assigned (1:1) by a computerised random number generator to laparoscopic gastric bypass or sleeve gastrectomy, with balanced block sizes of ten. Study personnel, participants, and the primary-outcome assessor were all masked to the allocation until 1 year after surgery, after which further follow-up was open label. Changes in key secondary outcomes, including type 2 diabetes remission, weight loss, and cardiovascular risk factors, were assessed 5 years after surgery. The trial procedure estimand assessed treatment effects in all randomised participants, with data collected after conversional surgery removed from analyses. The trial was registered with ClinicalTrials.gov (NCT01778738) and was completed in December, 2022. FINDINGS: Between Oct 15, 2012, and Sept 1, 2017, 319 patients were assessed for eligibility, resulting in 109 participants who were randomly assigned to gastric bypass (n=54) or sleeve gastrectomy (n=55). The baseline mean age was 47·7 years (SD 9·6), mean BMI 42·3 kg/m INTERPRETATION: Gastric bypass was superior to sleeve gastrectomy regarding long-term remission of type 2 diabetes, weight loss, and LDL cholesterol concentrations, at the expense of a higher frequency of symptomatic postprandial hypoglycaemia. These findings could inform clinical practice and future guidelines regarding the preferred surgical procedure in patients with type 2 diabetes. FUNDING: Vestfold Hospital Trust. TRANSLATION: For the Norwegian translation of the abstract see Supplementary Materials section.