Introduction: GLP1 receptor agonist lixisenatide has demonstrated its efficacy in numerous clinical trials, nevertheless its real-life effectiveness data is limited. Aim: To describe effectiveness and safety of lixisenatide in routine clinical practice in the Czech Republic and the Slovak Republic, as recorded by the Registry-Based Observational Study. Methods: Multinational, multicenter, observational, non-interventional, 6-month prospective product registry of patients with type 2 diabetes mellitus aged > 18 years who were initiating therapy with lixisenatide. Patients were enrolled into this registry, provided written informed consent, between 1 May 2013 and 31 December 2015. Evaluations were performed at baseline and after 3 and 6 months of lixisenatide treatment. The primary objective of the study was the absolute change in glycated hemoglobin (HbA 1c ) from baseline to month 6 after lixisenatide initiation. The study was approved by responsible ethics committees and performed in accordance with the Helsinki Declaration. Informed consent was obtained from all patients before enrolment in the study. Results: Overall 772 eligible patients (51.4 % males), mean age 56.7 (± 9.3) years, with mean diabetes duration 7.7 (± 5.5) years, mean duration of treatment with oral antidiabetic drugs 6.8 (± 4.9) years, and body mass index 37.6 (± 5.9) kg/m 2 were enrolled in the study. Overall, 93.6 % were obese, 86.3 % subject were treated for hypertension, and 76.0 % for dyslipidemia. In total 96.1 % of patients completed the 6 months' therapy. Lixisenatide significantly reduced HbA 1c (decrease by 9.7 ± 14.4 mmol/mol [3.1 ± 0.2 % DCCT] after 6 months in per protocol population), and body weight (decrease by 3.5 ± 5.4 kg). The best responders to the treatment were younger patients with higher BMI, who had a shorter duration of diabetes. Overall safety profile of lixisenatide was satisfactory in the study. The most frequent adverse events were functional disorders affecting the gastrointestinal system. There was no episode of severe hypoglycemia reported throughout the study. Conclusion: In a real-life practice cohort of patients with type 2 diabetes mellitus 6 months treatment with once-daily GLP1 receptor agonist lixisenatide significantly improved glucose control and decreased body weight without increasing the risk of symptomatic and/or severe hypoglycemia risk. Funding: Sanofi Czech Republic.