MPV (mean platelet volume) is one of the determinants of the platelet function which is situated in the routine complete blood count tests and was shown to be inversely correlated with inflammation. We aimed to evaluate MPV values in patients with peritoneal dialysis and in acute peritonitis attacks. 37 patients with PD and 42 healthy subjects were included in the study. 42 peritonitis attacks of the patients were recorded. C reactive protein (CRP) levels and complete blood count tests were analyzed. Mean MPV values were significantly higher in patients with PD in the stable period compared with the control group (p <0.001). Mean MPV values were significantly lower and CRP values were significantly higher in peritonitis attack periods, compared with the stable period of the same PD patients, both (p <0.001). In the correlation analysis, MPV levels in the peritonitis attack were negatively correlated with CRP levels, hospitalization day, peritoneal fluid and plasma leukocyte count (r= -0.751, p<0.001); (r= -0.355, p=0.002, ; ( r= -0.851, p<0.001) ; (r= - 0.579, p<0.001) respectively. In conclusion, our results suggest that assessment of MPV in acute peritonitis in PD patients may indicate systemic inflammation. MPV may be used as an hepler marker to predict the severity of acute peritonitis.