Aim: Our study aimed to evaluate the significance and clinical utility of immature granulocyte (IG) count (IGC) and IG percentage (IG%) in predicting attacks in patients with familial Mediterranean fever (FMF). Methods: This retrospective study included 100 FMF patients and 50 healthy controls. Data from 24 patients during the attack period and 76 patients during the attack-free period in the FMF group were obtained from medical records. Complete blood count analyses were carried out with the Mindray BC-6200 automated hematology analyzer following standard laboratory protocols. Receiver operating characteristic (ROC) curve analysis was conducted to differentiate FMF patients in the attack period from those in the attack-free period. Results: In FMF patients, levels of WBC (p = 0.032), neutrophils (p = 0.001), C-reactive protein (CRP) (p = 0.002), IG count (p < 0.001), and IG percentage (p < 0.001) were significantly higher compared to healthy controls. During the attack period, IG count and IG percentage levels were significantly elevated compared to the attack-free period (p < 0.001 for both). Based on ROC analysis, IG count and IG percentage showed significant diagnostic potential in FMF patients, with AUC values of 0.841 and 0.766, respectively. Conclusion: IGC and IG% serve as indicators of inflammation in FMF patients and may facilitate the differential diagnosis of FMF attacks, with respective cut-off values of 0.04 × 109/L and 0.4%. Given their accessibility and lack of additional cost, these parameters have the potential to enhance clinical practice by augmenting the diagnostic utility of conventional inflammatory biomarkers.