This study will investigate the efficacy and safety of the BI 10773 in type 2 diabetic patients with renal impairment in order to provide these data for approval for BI 10773 as an antidiabetic agent by regulatory authorities.

Inclusion criteria:

1. Diagnosis of type 2 diabetes mellitus prior to informed consent and an estimated glomerular filtration rate of <90 ml/min.
2. Male and female patients on diet and exercise regimen who are pre-treated with any antidiabetic therapy and are on the maximum tolerated dose which has been unchanged for 12 weeks prior to randomisation.
3. HbA1c greater than or equal to 7.0% and less than or equal to 10.0% .
4. Aged 18 years or above.
5. Body Mass Index less than or equal to 45 kg/m2

Exclusion criteria:

1. Uncontrolled hyperglycaemia defined as >13.3 mmol/L after an overnight fast during placebo run-in.
2. Impaired renal function, defined as an estimated glomerular filtration rate <15 ml/min.
3. Renal impairment requiring any form of chronic dialysis.
4. Requiring acute dialysis within three months prior to informed consent.
5. Renal transplant recipient.
6. Myocardial infarction, stroke or Transient Ischemic Attack within three months prior to informed consent.
7. Indication of liver disease.
8. Bariatric surgery within the past two years.
9. Medical history of cancer.
10. Blood dyscrasias or any disorders causing hemolysis or unstable red blood cell.
11. Contraindications to pre-existing background antidiabetic therapy.
12. Treatment with anti-obesity drugs.
13. Current treatment with systemic steroids or change in dosage of thyroid hormones within six weeks prior to informed consent or any other uncontrolled endocrine disorder except Type 2 Diabetes.
14. Pre-menopausal women who are nursing or pregnant or are of child-bearing potential and are not practising an acceptable method of birth control.

Any publication of the result of this trial must be consistent with the Boehringer Ingelheim publication policy. The rights of the investigator and of the sponsor with regard to publication of the results of this trial are described in the investigator contract.