Our aim is to investigate the correlation between the mean platelet volume (MPV) levels and platelet counts of the septic children with 28-day mortality risk. MPV at admission (MPVadm), MPV at 72nd hour (MPV72h) and the difference between these two parameters (Delta MPV72h-adm) and platelet counts were recorded retrospectively. The control group consisted of 100 healthy children matched for age, gender, and ethnicity. One hundred eighty six children were enrolled into the study. The study group had significant higher MPV values than those of control group. There were 156 survivors and 32 nonsurvivors in study group with a mortality rate of 17%. Nonsurvivors had significantly higher MPVadm (p: 0.001), MPV72h (p: 0.001), Delta MPV72h-adm (p<0.001) and lower platelet count (p: 0.002) than survivors. MPVadm (OR 2.39), MPV72h (OR 4.23), Delta MPV72h-adm (OR 6.4), platelet count (OR 7.3), and need for mechanical ventilation support (OR 9.76) had significant effect on 28-day mortality risk at logistic regression analysis. At the receiver operating characteristic analysis (ROC) the cutoff values for MPVadm, MPV72h, and Delta MPV72h-adm were found to be 9 fL, 9.86 fL, and 0.79, respectively. Kaplan-Meier analysis and log-rank test proved that these cutoff values were significantly associated with the time of survival. Septic children who had high MPV levels at admission and whose MPV levels increased during follow up had higher risk of mortality. With the results of further researches targetting large groups of pediatric patients, MPVadm, MPV72h, and Delta MPV72h-adm values can be fast and reliable markers for early diagnosis of sepsis and mortality prediction.