© 2020, Duzce University Medical School. All rights reserved.Aim: Allergic proctocolitis (AP) is a common cause of rectal bleeding in infants. There is no diagnostic tool specific to the disease. The aim of the study was to evaluate hemogram parameters as a marker of inflammation in patients with AP. Material and Methods: The files of patients who were exclusively breastfed and diagnosed as food protein induced AP were examined retrospectively. A hundred and fifty patients diagnosed with AP were included in the study. The same number of healthy babies formed the control group. Parameters in complete blood count were compared between patient and control groups. Rectosigmoidoscopic examination was performed to confirm the diagnosis in patients who could not achieve complete improvement with diet therapy, and hemogram parameters were evaluated according to eosinophilic infiltration in biopsies. Results: The mean platelet volume (MPV) values (p<0.001) and eosinophil percentages (p=0.001) of the AP group were higher than the control group. The mean hemoglobin values of the AP group were statistically significantly lower than the control group (p<0.001). No statistically significant difference was found between patient and control groups in terms of white blood cell (WBC) count, platelet count, platelet distribution width (PDW) and neutrophil/lymphocyte ratio (NLR). WBC count, platelet count, hemoglobin, MPV and C-reactive protein (CRP) values were similar between groups of patients according to the number of eosinophils in colon biopsies. Conclusion: We observed a significantly higher MPV values and eosinophil percentages in patients with AP. These parameters maybe helpful in diagnosis of AP.