Objective: To study the state of insulin resistance which occurs in pregnancy and the possible role of cortisol in augmentation of this state.Design: Case-control study.Setting: Khartoum teaching hospital, Khartoum north hospital, Soba hospital, Ibrahim Malek hospital, maternity hospital and Fath-Elbasheer referral centre from January to August 19%.Subjects: Thirty pregnant women with gestational diabetes mellitus(GDM) and thirty pregnant women with impaired glucose tolerance(1GT) were compared with thirty control pregnant women with normal glucose tolerance.Results: The GDM and the IGT groups were found to have significantly higher levels of serum cortisol than that of the control group (937.2±79.4 nmol/l (mean f S.E.) and 794.2±60.5 vs 597.3±30.9 respectively, p < 0.0006].Conclusion: Cortisol has a great role to play in the deterioration of glucose tolerance in pregnancy