Objectives: The main objective of this study was to examine the influence of glucose and sodium levels on disease outcome in critically ill patients. Study design: This is a retrospective study. Participants and methods: The glucose and sodium concentrations of 283 patients in critical condition were monitored at the admission in the intensive care unit in Internal Clinic of the Clinical Hospital Centre Osijek. Results: Health problems most commonly diagnosed among patients are: acute renal insufficiency, sepsis and septic shock, coronary heart disease, cardiac decompensation, pneumonia and drug intoxication. Different levels of glucose and sodium have been found in some diagnoses. There is significantly lower glucose concentration in drug intoxication and acute renal insufficiency, while in sepsis and septic shock significantly higher sodium concentration. Glucose concentration did have a significant effect on the outcome. Significantly higher glucose levels are related to higher mortality rate. On the other hand, the sodium concentrations did not have a significant effect on the outcome of the disease. Patients older than 65 years had significantly more deaths and elevated glucose levels. No significant differences were found in gender-related outcome, while the age of patients had an impact on outcome. Conclusion: Differences in glucose and sodium concentration were found in individual diagnoses. The study shows that there are no significant differences in sodium concentrations with regard to the outcome of the disease. The results of this study imply that significantly higher glucose levels are related to higher mortality rate. Glucose is a better predictive factor in disease outcomes in critical condition while sodium has lower values as a predictive factor.