Familial Mediterranean fever (FMF) is an autosomal recessive disorder characterized by intermittent episodes of fever with serositis, arthritis, or eriseplemya. Plasminogen activator inhibitor 1 (PAI-1) is a key element in the inhibition of fibrinolysis by inactivating tissue-type and urokinase-type plasminogen activators. We evaluated the association of PAI-1 -675 4G/5G polymorphism with the severity of FMF disease. For this purpose, 89 FMF patients with M694V homozygous mutation and 95 healthy controls from Iranian Azeri Turks were selected. Detection of this polymorphism was performed by polymerase chain reaction using allele-specific primers. No significant association was found between patients and control group. However, these data showed that FMF patients with M694V homozygous mutation carrying 4G/4G genotype have a reduced risk for development of pleuritis (odds ratios (OR) 0.36; 95 % confidence intervals (CI) 0.5-0.85; P value = 0.007) compared with 5G/5G homozygotes who have increased risk for development of amyloidosis (OR = 2.46; 95 %CI = 1.29-4.72; P value = 0.001), pleuritis (OR = 2.55; 95 %CI = 1.31-4.99; P value = 0.001), and fever (OR = 4.68; 95 %CI = 2.04-10.96; P value = 0.000). Furthermore, the allelic frequency of the 4G among the patients with pleuritis was significantly low (OR = 0.5, 95 % CI = 0.27-0.92, P value = 0.008).Our data suggest a protective role for the 4G allele against pleuritis in FMF patients with M694V homozygous mutation in this cohort. More evaluation of this polymorphism may be important and require further studies.