Aims Familial Mediterranean fever (FMF) is an autosomal recessive disorder characterised by recurrent episodes of fever and serosal inflammation with elevated acute phase reactants. Assessing the severity of the disease may be useful in identifying colchicine-resistant patients. The aim of this study is to determine the disease severity of FMF patients according to the Pras, Mor, and International Severity Scoring System for Familial Mediterranean Fever (ISSF) scoring systems and to evaluate the consistency of these three systems. Methods The medical records of patients with FMF were retrospectively reviewed. Demographic features, family history of FMF, clinical characteristics at disease onset, laboratory features, Mediterranean fever genetic mutations, treatment regimens, and disease courses were recorded. Results A total of 205 patients (116 girls) were included in the study. The mean age of the patients was 13.3 +/- 4.0 years. The Pras, Mor, and ISSF scores were inconsistent with each other, and there was poor fit between them (generalised Kappa: 0.140 +/- 0.029; P < .001). In the receiver operating characteristic (ROC) analysis performed by accepting the clinician's opinion as the gold standard, the ISSF was found to be more sensitive and specific than the other two systems. Conclusion Evaluation of disease severity according to the ISSF in paediatric patients is more sensitive and specific than the Pras and Mor scoring systems.