Objective To formulate an evidence-based treatment plan for a patient with gestational diabetes mellitus. Methods Based on the clinical questions raised from a real-life patient of gestational diabetes mellitus, we searched ACP Journal Club (1991 to Dec. 2006), The Cochrane Library (Issue 4, 2006), MEDLINE (1966 to Dec. 2006) and Chinese Biological Medical Database (1980 to Dec. 2006) for systematic reviews, randomized controlled trials, cohort and case-control studies. We used the following keywords: gestational diabetes, metformin, and pregnancy complication. The quality of the included studies was assessed.Results One meta-analysis (from MEDLINE) and two randomized controlled trials (from the Cochrane Central Register of Controlled Trials) were included. These studies concluded that there was no clear evidence on the benefits of metformin for gestational diabetes. Based on the current evidence, integrated with clinical expertise and the patient’s values, metformin was not used for this patient. Instead, intensive dietary control, blood glucose control, and appropriate exercise were administered. After this individual treatment, the patient gave birth to a healthy baby in 39+4 Weeks. Conclusion The appropriate management for gestational diabetes mellitus has been formulated with the approach of evidence-based medicine. Large-scale, methodologically-sound trials are required.