Gestational diabetes mellitus (GDM) is one of the most common clinical issues facing obstetricians and their patients. A lack of data from well-designed studies has contributed to the controversy surrounding the diagnosis and management of this condition. The purpose of this document is to provide a brief overview of our understanding of GDM and provide management guidelines that have been validated by appropriately conducted clinical research. When outcomes-based research is not available, expert opinion is provided to aid the practitioner.