Background: According to the World Health Organization, Mexico presents one of the highest mortality rates due to coronavirus disease 2019 (COVID-19). The "cytokine storm" phenomenon has been proposed as a pathological hallmark of severe COVID-19. Objective: To determine the association of serum cytokine levels with COVID-19 severity. Methods: We studied the cytokines IL-2, IL-4, IL-6, IL-10, TNF-α, and the IFN-γ serum levels through flow cytometry in 56 COVID-19 patients (24 critical and 32 non-critical) from Northwest Mexico. Results: We observed a significant increase in the IL-6 and the IL-10 levels in the sera of critical patients. These cytokines were also associated with mechanical ventilation necessity and death, IL-6 showing AUC values above 0.7 for both variables; and correlated with Na+, creatinine, and platelet levels. On the other hand, no association was found between IL-2, IL-4, TNF-α, and IFN-γ with tested variables. Conclusion: Our results corroborate previous observations regarding IL-6 and IL-10 involvement in the severity of COVID-19.