Introduction: The importance of screening for diabetes mellitus is a contruversial issue worldwide; its vitality is obvious when it leads to effective treatment for those identified at screening. This study was performed in Isfahan city to evaluate quality of care and treatment one year after diagnosis, in diabetic patients, newly diagnosed by screening. Materials and Methods: In this prospective study, 1640 adults were screened for diabetes in the Isfahan endocrine and metabolism research center, 2003-2004. Height, weight, blood pressure, plasma glucose, lipids, and HbA1c of diabetic patients, who identified at screening, were measured twice, once, at time of diagnosis and then again one year later. The results of the two measurements were compared. Furthermore quality of care and treatment of patients were evaluated. Results: Eighty-three (5.06%) of 1640 adults, were diagnosed as having diabetes. The prevalence's of dyslipidemia and hypertension among diabetic patients were 78.3% and 45% respectively. One year after diagnosis 77.1% of diabetic patients were treated for hyperglycemia, whereas 49.2% of dyslipidemic and 45% of hypertensive patients were treated for dyslipidemia and hypertension respectively. After one year, patients had significant improvements in BMI, plasma glucose, lipids and HbA1c but no improvements were seen in systolic and diastolic blood pressure. Conclusion: Diabetes screening is effective for detection of undiagnosed diabetes and improvement of glucose and control of other cardiovascular risk factors. It seems that quality of care and treatment, especially hypertension management, needs to be improved.