OBJECTIVE: The Exenatide BID Observational Study (ExOS) was designed to evaluate the clinical effectiveness of exenatide BID use in patients with type 2 diabetes (T2D) in a real-world clinical practice setting in the United States. METHODS: Patients were enrolled from 74 practice sites from 9/2007 through 1/2009 and followed for 12 months. The primary effectiveness endpoint was achieving or maintaining hemoglobin A1C of =7.0%, or an absolute drop of 0.5% from baseline. Secondary measures included absolute and percentage change from baseline for a variety of clinical measures (lipid markers, weight, BMI, etc.), and quality of life (QOL) was assessed using the Impact of Weight on Quality of Life (IWQOL)-Lite. RESULTS: A total of 452 patients were included in the primary study population. At baseline, patients (60% female) had mean (SD) age of 55 (11), T2D duration of 9 (8) years, HbA1c of 8.0 (1.7) %, and body mass index (BMI) of 38.2 (7.4) kg/m(2). Family history of T2D was reported in 73.9% of patients. Hypertension was reported in 61.5% of patients, and 47.1% had hyperlipidemia. The HbA1c goal was achieved in 76.3% of the 118 patients with A1C measurements available at 12 months (P < 0.0001). Patients with available clinical measurements achieved significant improvements in HbA1c, weight, BMI, and QOL measurements at 12 months. A mean improvement of 4.56 was seen in the total IWQOL-Lite score at 12 months (P = 0.001). The single-arm design of this study is a limitation; however, the overall objective of the study was to observe patients on exenatide BID therapy over time, comparing their status at endpoint to baseline, rather than to make comparisons among different drug therapies. CONCLUSIONS: The Exenatide BID Observational Study supports the clinical effectiveness of exenatide BID observed in previous clinical trials and retrospective database studies.