The diagnostic score for acute appendicitis was constructed by logistic regression analysis. Continuous laboratory values (CRP, leukocyte count and proportion of neutrophils) were categorized into 4 categories. Cut-off points for the categories were determined by using receiver operating characteristics (ROC) analysis. Cut-off for abnormal body temperature was determined using ROC analysis. Because the distributions of CRP values were significantly different in patients with symptoms less than 24 hours and in patients with symptoms more than 24 hours the cut-off values for CRP were determined in these 2 subsets of patients separately. A multiple imputation for missing neutrophil and CRP data was done. A backward logistic regression analysis included all signs and symptoms, duration of symptoms and categorized laboratory values. Duration of symptoms was used as a variable and an interaction term with categorized CRP values. Being a fertile aged woman (16–49 years old) was included as a variable and an interaction term for all signs and symptoms. Final step of backward stepwise logistic regression with multiple imputed pooled data resulted in statistically significant factors for construction of the score. Points for the score were obtained from regression coefficients by multiplying by 2 and rounding to the nearest integer. Please see Additional file 1 for a table of regression coefficients and the resulting points of the score.