Aims: The aim of this study is to evaluate our patients with the newly developed international severity score for FMF (ISSF) and make comparisons with the literature. Methods: This cross-sectional study included patients with FMF, were between 6 months and 18 years old, and were using colchicine/colchicine+IL-1 inhibitor for at least 6 months. The patients were classified as mild, intermediate, and severe based on their scores between 1 and 10. In addition to scoring, those who have additional pathological or silent mutation were compared based on these classifications. Results: Our patients consist of 88 women 72 men total 160. The mean age, age of onset, and age of diagnosis were 12 ± 4.3, 4.9 ± 3.7, and 7.5 ± 4 years, respectively, and the mean diagnostic delay was 2.6 ± 3years. When our large patient population is evaluated with ISSF, the disease severity is mostly intermediate. According to ISSF, mild, intermediate, and severe diseases were 21.3%, 70.5%, and 8.1%, respectively. The duration of attacks shorten with increasing age (p > 0.05), and there is an increase in the involvement of other organs during the attacks among patients older than 7 years. Conclusions: ISSF appears as a suitable and effective tool for the physicians in the follow-up of the disease severity in pediatric FMF patients.Key Points•Our article is the first study to evaluate ISSF performance in the pediatric population.•International severity score for FMF (ISSF) appears as a suitable and effective tool for the physicians in the follow-up of the disease severity in pediatric FMF patients.•We think that the addition of pathogenic mutations and inheritance model to the ISSF scoring system as important determinants of disease severity, especially when comparing different patients, can be evaluated in future studies.