Introduction: Management of type 2 diabetes mellitus (T2DM) in patients with chronic kidney disease is complex. Using the REALI European pooled database, we determined the impact of baseline renal function on the effectiveness and safety of insulin glargine 300 U/mL (Gla-300) initiated in adults with inadequately controlled T2DM. Methods: Data from 1712 patients with available estimated glomerular filtration rate (eGFR) at baseline were pooled from six 24-week prospective studies. Patients who received once-daily subcutaneous injections of Gla-300 were classified into four renal function subgroups, according to baseline eGFR: C 90 (N = 599), 60-89 (N = 786), 45-59 (N = 219), and 15-44 mL/min/1.73 m 2 (N = 108). Results: Compared to those with baseline eGFR C 60 mL/min/1.73 m 2 , patients with lower eGFR values tended to be older, had a longer T2DM duration, and were more likely to present diabetic complications. After 24 weeks of Gla-300 therapy, the least-squares mean (95% confidence interval) decrease in haemoglobin A1c (HbA1c) from baseline (-1.14% [