Aim. Ascitic fluid infection (AFI) consists primarily of two variants, namely, culture-negative neutrocytic ascites and spontaneous bacterial peritonitis (SBP). Mean platelet volume (MPV) has begun to be used as a simple and inexpensive indicator of inflammation in some diseases. We aimed to analyse whether platelet size alterations would be useful in predicting AFI in cirrhotic patients. Material and methods. A total of 135 patients with ascites due to cirrhosis and 55 control subjects were enrolled in this study. According to ascitic fluid analysis, 58 patients were considered to have AFI. MPV and inflammatory parameter values were determined for all, study participants. The ability of MPV values to predict AFI in cirrhotic patients was analysed using receiver operator characteristic (ROC) curve analysis. Results. A statistically significant increase in MPV levels was observed in cirrhotic patients with AFI compared to cirrhotic patients without AFI and healthy controls (p < 0.001). A statistically significant increase was observed in the AFI group with respect to MPV, C-reactive protein (CRP) and white blood cell (WBC) levels. ROC curve analysis suggested that the optimum MPV level cut-off point for cirrhotic patients with AFI was 8.45, with a sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of 70.7%, 67.5%, 75.4% and 62.1%, respectively (area under curve: 0.768). Conclusion. Our study shows that MPV is increased in cirrhotic patients with AFI. MPV measurement can considered to be an accurate diagnostic test in predicting AFI, possibly due to an ongoing systemic inflammatory response.