A method for reducing the incidence or delaying the onset of diabetes in diabetes-susceptible mammals (e.g., mice, rats, humans) is provided wherein the mammals are treated with a gonadotropin-releasing hormone (GnRH) antagonist. Additionally, the present invention provides a method of prolonging the honeymoon phase and decreasing the rate of islet cell infiltration by lymphocytes by administration of a GnRH antagonist. Preferably, the antagonist is administered repeatedly over time by subcutaneous injection. Preferred antagonists include Acetyl-β-[2-Naphthyl]-D-Ala-D-p-Chloro-Phe-β-[3-Pyridyl]-D-Ala-Ser-Nε-[Nicotinoyl]-Lys-Nε-[Nicotinoyl]-D-Lys-Leu-Nε-[Isopropyl]-Lys-Pro-D-Ala-NH2, Nal-Glu, Abarelix, Degarelix, and acetyl-D2Nal-D4CIPhe-D3Pal-Ser-Aph(Ac)-D-Aph(Ac)-Leu-Lys(lpr)-Pro-D-Ala-NH2.