Purpose Catarrhal appendicitis (CA) could be treated effectively with antibiotics in some patients because of the milder inflammation associated with this form of appendicitis. Although several trials have compared surgery with antibiotic therapy for acute appendicitis (AA), the indications for antibiotic therapy remain controversial. Methods The subjects of this study were 342 patients who underwent appendectomy at our hospital between January, 2000 and March, 2013. The patients were divided into two groups based on the severity of their appendicitis: Group A comprised patients with severe appendicitis and Group B comprised patients with CA. Statistical analyses were performed to assess the clinical features associated with CA. Results Multivariate analysis of the eight clinical features correlated with CA according to univariate analysis revealed that the neutrophil to lymphocyte ratio (NLR) ( < 5/>5), age ( < 38/>38 years), fever ( < 38/>38 °C), white blood cell count ( < 11.5/>11.5 × 10 3 /mm 3 ) and serum level of C-reactive protein ( < 110/>110 mg/L) were significantly associated with CA. The NLR ( < 5/>5) (OR 0.421; 95 % CI 0.218–0.811; P  = 0.010) was the most useful predictor of CA, because the area under the ROC curve of NLR was the lowest of all these features. Conclusion The preoperative NLR in patients undergoing appendectomy is closely associated with CA.