PURPOSE: The pathophysiology, diagnosis, complications, and management of gestational diabetes mellitus (GDM) are discussed, along with considerations in setting up a pharmacist-run GDM education service. SUMMARY: GDM occurs when there is insufficient insulin secretion to counteract pregnancy-related decreases in insulin sensitivity. GDM can be diagnosed by using the same criteria used to diagnose types 1 and 2 diabetes mellitus (DM): a fasting blood glucose concentration of > 126 mg/dL on two separate occasions or a random blood glucose concentration of > 200 mg/dL on two separate occasions. Complications of GDM include maternal type 2 DM, maternal hypertension, macrosomia, shoulder dystocia, and neonatal hypoglycemia. GDM is managed with medical nutritional therapy (MNT), exercise, and therapy with human or synthetic insulin. The American Diabetes Association recommends starting insulin therapy when MNT fails to maintain plasma glucose concentrations at < or = 105 mg/dL during fasting, < or = 155 mg/dL one hour after eating, or < or = 130 mg/dL two hours after eating. A pharmacist interested in establishing a GDM education service must assess the feasibility of providing such education in his or her practice and whether such a program is needed. Other considerations are developing a curriculum, marketing the service, maintaining records, calculating costs, and obtaining reimbursement. CONCLUSION: GDM can have serious effects if not treated properly. A major part of managing GDM involves educating the patient about diet, exercise, blood glucose self-monitoring, and insulin self-administration. A successful pharmacist-run GDM education service must have a market and prices sufficient to generate profit.