In our study we aimed to assess the clinical significance of the mean platelet volume as an early diagnostic marker in diagnosis of spontaneous bacterial peritonitis. A total of 60 patients with ascites due to cirrhosis and 10 control subjects were enrolled in this study. According to ascitic fluid analysis, 30 patients were considered to have SBP. All patients were subjected to history taken, complete clinical examination, routine laboratory investigations, mean platelet volume, chemical and physical analysis of ascitic fluid, abdominal ultrasound. Comparison between three groups showed significantly higher mean platelet volume in patients with SBP with mean level of 10.8 ±1.3 fl in SBP group. A statistically significant increase in MPV levels was observed in cirrhotic patients with SBP compared to cirrhotic patients without AFI and healthy controls (P