OBJECTIVE: This study was conducted to demonstrate the efficacy and safety of LixiLan (iGlarLixi), a novel, titratable, fixed-ratio combination of insulin glargine (iGlar) (100 units) and lixisenatide, compared with iGlar in patients with type 2 diabetes inadequately controlled on basal insulin with or without up to two oral glucose-lowering agents. RESEARCH DESIGN AND METHODS: After a 6-week run-in when iGlar was introduced and/or further titrated, and oral antidiabetic drugs other than metformin were stopped, 736 basal insulin-treated patients (mean diabetes duration 12 years, BMI 31 kg/m2) were randomized 1:1 to open-label, once-daily iGlarLixi or iGlar, both titrated to fasting plasma glucose <100 mg/dL (<5.6 mmol/mol) up to a maximum dose of 60 units/day. The primary outcome was change in HbA1c levels at 30 weeks. RESULTS: HbA1c decreased from 8.5% (69 mmol/mol) to 8.1% (65 mmol/mol) during the run-in period. After randomization, iGlarLixi showed greater reductions in HbA1c from baseline compared with iGlar (-1.1% vs. -0.6%, P < 0.0001), reaching a mean final HbA1c of 6.9% (52 mmol/mol) compared with 7.5% (58 mmol/mol) for iGlar. HbA1c <7.0% (53 mmol/mol) was achieved in 55% of iGlarLixi patients compared with 30% on iGlar. Mean body weight decreased by 0.7 kg with iGlarLixi and increased by 0.7 kg with iGlar (1.4 kg difference, P < 0.0001). Documented symptomatic hypoglycemia (=70 mg/dL) was comparable between groups. Mild gastrointestinal adverse effects were very low but more frequent with iGlarLixi. CONCLUSIONS: Compared with iGlar, a substantially higher proportion of iGlarLixi-treated patients achieved glycemic targets with a beneficial effect on body weight, no additional risk of hypoglycemia, and low levels of gastrointestinal adverse effects in inadequately controlled, basal insulin-treated, long-standing type 2 diabetes.