Abstract Background Some evidence has provided that electrolyte disorders may be present upon presentation of patients with COVID-19 infection. We investigated serum sodium, potassium, calcium, magnesium, and phosphorus levels in large numbers of critically ill COVID-19 patients to identify its possible prognostic value in these patients. Methods This retrospective study included patients confirmed with COVID-19 infection admitted to critical care units of Zagazig University Hospital all over 1 year, from May 1, 2020, to April 30, 2021. We analyzed the data for possible correlations between serum electrolytes and patients’ outcomes. Results Among 600 patients included in the study with a mean age of 51.33 ± 16.5 years, 44.16% were mechanically ventilated, and 30.66% died during hospital admission. Serum sodium, potassium, phosphorus, magnesium, and calcium were 141.96 ± 5.4, 4.33 ± 0.66, 3.76 ± 1.26, 2.21 ± 0.52, and 8.55 ± 0.85 respectively, at admission to the ICU. Unfavorable admission course and mortality were significantly associated with high normal serum sodium, potassium, and phosphorus levels and a low normal calcium level. Conclusion Although mean serum sodium, potassium, calcium, magnesium, and phosphorus were within normal levels in patients with COVID-19 at presentation, serum sodium, potassium, and phosphorus were significantly higher in those with poor outcomes, whereas calcium was significantly lower in those with poor outcomes. Keywords COVID-19, Electrolytes, Prognosis, Outcome