In the EDITION clinical trial programme, patients with type 2 diabetes mellitus (T2DM) receiving insulin glargine (IGlar) U300 required 10-15% more insulin than those receiving IGlar U100. This study sought to determine whether this difference was apparent in real-world practice. In this observational, retrospective cohort study, electronic medical records in the Big-Pac® database (Real Life Data) relating to adult insulin-naïve patients with T2DM who initiated IGlar U100 or U300 treatment in Spain in 2016-2017 and remained on treatment for 18 months were selected. IGlar U100- and U300-treated patients were matched 1:1 (propensity score matching). The primary analysis compared changes from baseline in mean daily IGlar dose (U and U/kg) at 6 (± 2), 12 (± 2) and 18 (± 2) months between cohorts (paired t tests). Changes in glycated haemoglobin (HbA1c) and weight were analysed descriptively. The IGlar U100 and U300 cohorts included 556 matched pairs (46.9% female) with the following mean (standard deviation) values at baseline, respectively: age 63.6 (12.8) versus 63.7 (11.9) years; years since diagnosis 9.5 (1.4) versus 9.5 (1.3); HbA1c 8.8 (1.3) versus 8.7 (1.5) %; weight 84.6 (16.9) versus 84.7 (17.1) kg. Mean IGlar dose at baseline was 0.19 U/kg/day (both cohorts). Patients receiving IGlar U300 showed a greater increase from baseline in IGlar dose at 6, 12 and 18 months [mean dose (U/kg/day) 5.1%, 10.3% and 12.8% greater, respectively, in IGlar U300-treated patients]. Mean HbA1c was 8.1% in both cohorts at 18 months. Mean (SD) weight at 18 months with IGlar U100 and IGlar300 was 86.8 (17.0) kg and 85.0 (17.1) kg, respectively. In real-world practice, insulin dose was significantly higher in IGlar U300-treated than U100-treated patients at 6, 12 and 18 months, with similar reductions in HbA1c. At equal IGlar price/unit in Spain, the increased dose requirements of IGlar U300 would result in higher costs. The online version contains supplementary material.