Background and Objectives: Sleep deprivation and coffee caffeine consumption have been shown to affect glu- cose homeostasis separately, but the combined effects of these two variables are unknown. Methods and Study Design: Forty-two healthy Iranian men, aged 20-40 years old, were assigned to three groups in a randomised crossover trial involving three treatments with two-week washout periods. Subjects were moderate coffee con- sumers (≤3 cups/day), and had a Pittsburgh Sleep Quality Index ≤5. Each treatment involved three nights of de- prived sleep (4 hrs. in bed) plus 3×150 cc/cup of boiled water (BW treatment), decaffeinated coffee (DC treat- ment, without sugar, 99.9% caffeine-free), and caffeinated coffee (CC treatment, without sugar, 65 mg caf- feine/cup). DC and CC treatments were blinded. At the end of each treatment, fasting serum glucose (using en- zyme assays) and insulin (using electrochemiluminescence immunoassay) were measured and, again, two hours after an oral glucose tolerance test (OGTT). Insulin resistance was quantified with the homeostasis model. Re- sults: Repeated measures ANOVA indicated no significant difference between the treatments in fasting serum glucose (p=0.248) or insulin resistance (p=0.079). However, ANOVA demonstrated differences between treat- ments in fasting serum insulin (p=0.004) and glucose, as well as insulin after OGTT (p<0.001). Pairwise compar- isons test (within subjects) showed that the CC treatment yielded higher serum glucose and insulin after OGTT (p<0.001), higher fasting serum insulin (p=0.001), and increased insulin resistance (p=0.039) as compared to the DC treatment. Conclusions: Thus caffeinated coffee was more adverse for glucose homeostasis compared to de- caffeinated coffee in individuals who were simultaneously sleep deprived.