The aim of this study is to investigate the diagnostic efficacy of neutrophil-to-lymphocyte ratio (NLR), neutrophil-to-monocyte ratio (NMR), lymphocyte-to-monocyte ratio (LMR), and platelet-to-lymphocyte ratio (PLR) in patients with Crohn's disease (CD) and non-CD controls. These ratios were all derived from complete blood counts. Two hundred and six participants including CD inpatients and non-CD controls were retrospectively enrolled. We found statistically higher NLR and PLR and lower LMR in CD patients than in non-CD controls (all P < 0.01). However, NMR was not different between the two groups (P = 0.18). In addition, NLR, PLR, and LMR were associated with CRP and ESR. Optimal cutoffs for NLR and PLR were 2.72 (sensitivity: 68.3%, specificity: 75.9%, and overall accuracy: 70.1%) and 132.88 (sensitivity: 76.7%, specificity: 84.8%, and overall accuracy: 80.8%), respectively. In conclusion, the NLR and PLR might be effective, readily available, and low-cost biomarkers for differentiating CD patients from non-CD controls.