Introduction: Multiple myeloma (MM) is a hematological malignancy characterized by the presence of abnormal clonal plasma cells in the bone marrow. Immunodeficiency seen in patients with multiple myeloma (MM) is a serious problem. Blastocystis sp. is found in the gastrointestinal tract and can infect humans. Background/ Aims: In our study, we compared the prevalence of B.hominis and other parasites with the control group and patients who had recently been diagnosed with multiple myeloma. Material-Methods: Ninety-five multiple myeloma patients from our center and 95 volunteers as a control group were included in our study. The patients did not have any symptoms when stool samples were taken. For B.hominis, three consecutive stool samples were examined by saline-lugol trichrome staining and formalin-ethyl acetate concentration. Data were recorded and analyzed using SPSS 25.0. Results: Patients with newly diagnosed multiple myeloma and any of the patients in the control group did not have any parasites other than B.hominis. A significant difference was found between the newly diagnosed MM patients and the control group in terms of the number of B.hominis occurrences in the stool (p <0.001). Conclusions: According to this result, parasite load in stool increased in patients with MM. This result may reflect the suppression of the immune system of patients with MM. Accordingly, B.hominis should be considered as a causative agent in the presence of gastrointestinal symptoms that may occur during treatment in patients with MM.