Background and Objective: Familial Mediterranean Fever (FMF) is an autosomal recessive disorder characterized by self-limited episodes of fevere and painful recurrent polyserositis that predominantly affects Mediterranean races. In recent years some reports have shown high prevalence of FMF in North-west Iran, with M694V and E148Q being most frequent reported mutations. The aim of this study is to evaluate the clinical manifestations of FMF in patients with these mutations. Materials and Methods: A cross sectional- descriptive study was performed in a 1 year period (January 2007 – January 2008). 71 patients younger than 18 years with clinical diagnosis of disease proved in Children Hospital of Tabriz-Iran were referred to genetic lab for mutation analysis. ARMS-PCR & PCR-RFLP were used to detect mutations. Only 45 patients were shown to have identified mutations and 41 patients among them had M694V and E148Q mutations which were assessed for various clinical manifestations. Results: M694V and E148Q mutations were seen in 55.7% and 35.5% patients respectively. Patients homozygous for M694V were found to have earlier age of onset, longer duration of attacks, higher prevalence of positive family history and more complications. In our patients, prevalence of some manifestations differed from other ethnic groups reported previously. Conclusions: M694V mutation in FMF patients especially in homozygous state is accompanied with more severe disease and more complications.