In this study, our aim was to examine the diagnostic and prognostic significance of lymphocyte/C-reactive protein ratio (LCR), neutrophil/lymphocyte ratio (NLR) and D-dimer parameters in COVID-19 infection. The LCR, NLR, neutrophil count, mean platelet volume (MPV), C-reactive protein (CRP), and D-dimer parameters were evaluated retrospectively. This was a retrospective cohort study with 1000 COVID-19 positive and 1000 healthy control groups, all over the age of 18 years. Odds ratio (OR) and 95% confidence interval (CI) values were calculated for each parameter found to be statistically significant in the univariate and multivariate logistic regression models.Herein, 127 (12.7%) of the COVID-19 + patients, whose data was included in this study, died. The neutrophil, MPV, CRP, D-dimer, and NLR values were higher in the COVID-19 + /deceased group than in the COVID-19 + /alive and control groups (p < 0.001, p < 0.001, p < 0.001, p < 0.001, p < 0.001). The lymphocyte and LCR values were lower in the COVID-19 + /deceased group than in the COVID-19 + /alive and control groups (p < 0.001, p < 0.001). Variables with statistically significance in predicting COVID-19 infection were lymphocyte, LCR, D-dimer, NLR, CRP, MPV, PLT, and neutrophil values. Statistically significant variables in predicting mortality due to COVID-19 were LCR, CRP, NLR, lymphocyte, D-dimer, neutrophil, and MPV values. A low LCR and high NLR are associated with the presence, prognosis, and mortality due to COVID-19. LCR and NLR parameters can thus be used in clinical monitoring to reduce morbidity and mortality rates.