Objective Based on the methodology of evidence-based medicine, we explored the prognosis of a patient with gestational diabetes mellitus (GDM). Methods We searched ACP Journal Club (1991 to October 2006), The Cochrane Library (Issue 4, 2006), MEDLINE (1990 to October 2006) and Chinese Biomedicine database (CBM). Cohort studies, case-control studies and case series studies involving the prognosis of patients with GDM were collected. The available evidence was critically appraised. Results During the period from 6 weeks to 28 years after delivery, the incidence of type 2 diabetes mellitus appeared to vary from 2.6% to 70%. Patients with GDM suffered from an increased incidence of spontaneous premature delivery, hypertension, metabolic syndrome and vaginal infection. Conclusion Patients with GDM appears to be more liable to overt diabetes mellitus, and to suffer fromspontaneous premature delivery, hypertension, metabolic syndrome and vaginal infection than women with normal glucose tolerance during pregnancy. Further studies of the long-term follow-up data from GDM trials are needed.