The objective of this study was to assess insulin sensitivity and cortisol concentration in healthy subjects with 24-hr sleep deprivation. A randomised, single-blind, controlled clinical trial was performed in 28 healthy subjects. Fourteen individuals were studied before and after 24-hr sleep deprivation and 14 volunteers with normal sleep periods (NSP) as a control group. Serum creatinine, uric acid, total cholesterol, high-density lipoprotein cholesterol, and triglyceride concentrations were measured in both groups. Insulin suppression test modified with octreotide (IST) and cortisol levels were performed before and after 24-hr sleep deprivation or NSP. Clinical and metabolic characteristics of the subjects in both groups are similar. Steady-state glucose (SSG) concentration of the IST was significantly higher after 24-hr sleep deprivation (5.7+/-2.1 vs 6.7+/-2.2 mmol/l; p=0.01). SSG level was similar before and after NSP (5.0+/-2.1 vs 5.0+/-1.8 mmol/l, respectively; p=0.91). There were not significant differences in cortisol levels between initial and final tests in both groups. In conclusion, 24-hr sleep deprivation decreased the insulin sensitivity in healthy subjects without changes in cortisol levels.