Objective: The primary aim of type 2 diabetes (T2D) therapy is helping patients achieve glycemic goals (A1C<7%) as recommended by the ADA. In the recent randomized controlled trials 4-T and INITIATE, patients treated with basal insulin alone achieved goal 28% and 40% of the time, respectively, despite progressive insulin titration. In this retrospective cohort study using a large, US commercial health plan claims database, we describe the clinical effectiveness of newly-prescribed basal insulin glargine (IG) in insulin-naive patients. Methods: A total of 13,154 insulin-naïve (not prescribed insulin in previous 6mo) patients were identified with a new prescription claim for IG between January 1, 2004 and June 30, 2006, =6mo of pre-index eligibility (first claim=index date), =12mo of post-index eligibility, and =18y old. Results: From this cohort, 7730 (59%) patients had no other insulin claims other than IG in the entire post-index period. All patients with baseline (100d pre-index) and post-index (60-365d) A1C data available and baseline A1C=7.0% were analyzed (n=313; mean baseline A1C (±SD)=9.8±2.1%). Mean (±SD) age was 52±8y (41% female; 3%=65y). In this cohort of patients who did not add any additional insulin (n=313), 27% achieved A1C <7% in the post-index period (mean [min,max] time index to post-index A1C=238d [63,365]). Mean (±SD) post-index A1C was 8.2±1.9%. Conclusion: In this real-world analysis of patients initiated on IG, the percentage of patients achieving A1C<7.0% and mean post-index A1C indicate that most patients do not achieve recommended glycemic targets—results which mirror controlled clinical studies. In addition, more than half of patients initiating IG did not supplement with additional insulin therapy over the course of the first year of therapy, despite not reaching glycemic goals. Because the contribution of postprandial glucose to A1C increases as A1C approaches goal, agents targeting fasting glucose alone, like IG, may be insufficient in helping patients with T2D achieve glycemic goals.