Eligible patients will receive vildagliptin 50 mg in addition to their stable dose of insulin with or without metformin. One tablet should be taken twice daily as one tablet before breakfast meal and one tablet before the evening meal for 24 weeks.

Eligible patients will receive matching placebo in addition to their stable dose of insulin with or without metformin. One tablet should be taken twice daily as one tablet before breakfast meal and one tablet before the evening meal for 24 weeks.

Patient will receive vildagliptin 50mg twice daily (bid) in addition to their stable dose of insulin with or without metformin for 24 weeks

HbA1c analysis will be performed on a blood sample obtained by study personnel at every visit and measured by ion exchange HPLC. Study endpoint is defined as final available post- randomization assessment obtained at any visit prior to or at the start of major change in insulin use, up to final scheduled study visit (week 24 visit) inclusive.

HbA1c analysis will be performed on a blood sample obtained by study personnel at every visit and measured by ion exchange HPLC. Study endpoint is defined as final available post- randomization assessment obtained at any visit prior to or at the start of major change in insulin use, up to final scheduled study visit (week 24 visit) inclusive.

Adverse events are defined as any unfavorable and unintended diagnosis, symptom, sign (including an abnormal laboratory finding), syndrome or disease which either occurs during study, having been absent at baseline, or, if present at baseline, appears to worsen. Serious adverse events are any untoward medical occurrences that result in death, are life threatening, require (or prolong) hospitalization, cause persistent or significant disability/incapacity, result in congenital anomalies or birth defects, or are other conditions which in judgment of investigators represent significant hazards.