Platelet (PLT) indices have been proposed as potential markers in the assessment of liver fibrosis and exacerbation of liver failure. The aim of our study was to verify mean platelet volume (MPV), platelet distribution width (PDW), and plateletcrit (PCT) in alcohol-related liver cirrhosis (ALC) and nonalcoholic fatty liver disease (NAFLD) patients. One hundred forty-two patients with ALC, 92 with NAFLD, and 68 in control group were enrolled in this study. Hematological indices (MPV, PCT, and PDW) and serological (indirect and direct) markers of liver fibrosis (AAR, APRI, FIB-4, GPR, PICP, PIIINP, TGF-α, PDGF-AB, laminin) were measured in each participant. MELD score in ALC patients and NAFLD fibrosis score (NFS) together with BARD score in the NAFLD group were also obtained. Results were compared between research and control groups. Then, a correlation between evaluated indices was performed in study groups. Receiver operating characteristic curves (ROCs) and area under the curve (AUC) values were applied to assess the diagnostic accuracy of measured indices. Significant increase in PDW and decrease in PCT in comparison to controls were noted in examined ALC (60.4% vs. 51.2% and 0.1% vs. 0.21%, respectively,p<0.0001) and NAFLD (54.75% vs. 51.2% and 0.19 vs. 0.21%, respectively,p<0.01) patients. Decreased level of MPV was observed in NAFLD group (7.85 fl vs. 8.90 fl,p<0.0001). Additionally, PCT correlated with NFS (p<0.0001). Evaluated PLT indices correlated with MELD score (MPV and PDW,p<0.001; PCT,p<0.05). They correlated with indirect and direct markers of liver fibrosis in the whole research group, too. PCT was the parameter with the greatest diagnostic accuracy in ALC patients (AUC=0,839forcutoff<0.17%); in NAFLD group, it was MPV (AUC=0,808forcutoff<7.9 fl). PCT in ALC and MPV in NAFLD can be perceived as potential diagnostic markers.