Video abstract: View a video abstract for this article. AIMS: This multicentre (N = 104), randomized controlled phase 4 study compared the efficacy and safety of insulin glargine 300 units/mL (Gla-300) with insulin glargine 100 units/mL (Gla-100) in patients with type 1 diabetes (T1D). MATERIALS AND METHODS: Patients were randomized 1:1 to self-perform morning Gla-300 or Gla-100 injections daily for 16 weeks. The primary endpoint was percentage of time blood glucose remained in the target range (70-180 mg/dL) during Week 15/16, measured by blinded continuous glucose monitoring. Secondary endpoints included incidence and rate of nocturnal symptomatic hypoglycaemia (