In the present study, the relationships between cortisol, cognitive function, depressive behavior, and sleep quality in chronic kidney disease (CKD) and hemodialysis (HD) patients was investigated. Patients underwent history taking, physical examination, biochemical analysis, 24-h urine collection (for CKD patients only), measurement of dialysis adequacy (for HD patients only), evaluation of cognitive function, depressive behavior and sleep quality. Among study participants 58 had creatinine clearance a parts per thousand yen60 mL/min/1.73 m(2) (Group 1), 41 had creatinine clearance between 30 and 59 mL/min/1.73 m(2) (Group 2), 25 had creatinine clearance between 15 and 29 mL/min/1.73 m(2) (Group 3) and 12 had creatinine clearance < 15 mL/min/1.73 m(2) (Group 4). 38 patients were regular HD patients (Group 5). The cortisol levels in Group 1, 2, 3, 4 and 5 patients were 472.3 +/- A 138.4, 490.2 +/- A 214.3, 541.6 +/- A 172.8, 569.9 +/- A 101.0 and 637.8 +/- A 153.7 nmol/L, respectively (P < 0.0001 for trend). In both non-dialysis patient group and dialysis patients linear regression analysis showed that cortisol was independently related with Beck depression inventory (BDI) score (P: 0.013 and 0.001, respectively) but not with cognitive function and sleep quality. In conclusion serum cortisol levels were independently associated with depressive behavior both in CKD and HD patients but not with cognitive function and sleep quality.