Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic disease that can be presented with fever, fatigue, generalized joint/body pain, diarrhea and bleeding in various parts of the body. The risk of developing a severe fatal disease in humans, the possibility of being infected with aerosols and the risk of being used as a biological weapon make the disease still an important health problem all over the world as there is no a specific treatment and vaccine that has proven effective againt the virus today. The pathogenesis of the disease is not known, but vascular endothelial damage is prominent. Therefore, it progresses with thrombocytopenia, anemia, leukopenia and this hematological findings can be confused with hematological malignancies. Acute lymphoblastic leukemia (ALL) is a malignancy included in differential diagnoses and occurs as a result of mutations occuring at a stage of differentiation in the lymphoid precursor cells in the bone marrow. In this study, we present a case of ALL who was diagnosed with CCHF simultaneously. A 43-year old female patient who works in the library and does not have a chronic disease other than asthma and thyroid disorder, has admitted to our hospital with the complaints of intermittent fever, weakness, generalized joint and body pain for about 3 weeks. She had fever and the physical examination revealed bilateral cervical and right postauricular lymphadenopathies. Her aspartate aminotransferase: 77 U/L, alanine aminotransferase: 117 U/L, lactate dehydrogenase: 616 U/L, hemoglobin: 8.27 g/dl, leukocyte count: 15.690/mm3 , neutrophil count: 550/mm3(%3.5), lymphocyte count: 6690/mm3(%42.6), platelet count: 102.100/mm3 , C-reactive protein: 163.6 mg/L was detected and the patient was hospitalized on 5 August 2019 for further examination and treatment. Considering that the patient may have viral infection in the foreground the requested test results were detected as; anti-CMV IgM negative, anti-CMV IgG positive, anti-toxoplasma IgM negative, anti-toxoplasma IgG positive, anti-rubella IgM negative, anti-rubella IgG positive, HBsAg negative, anti-HBc IgM negative, antiHBs positive, anti-HAV IgM negative, anti-HAV IgG positive, anti-HCV negative, anti-HIV negative, EpsteinBarr virus (EBV) VCA IgM negative, EBV VCA IgG positive, EBV EBNA IgG positive. Brucella Rose Bengal and Coombs tube agglutination was found be negative. As the cytopenia of the patient deepened, the patient was accepted to have neutropenic fever and it was planned to start piperacillin-tazobactam 4 x 4.5 g/day and two units of erythrocyte replacement therapy. When the patient’s history was questioned again, it was learned that she had a tick on her neck about three weeks ago and she had removed the tick herself; 4-5 days later she had the complaints of fever and flu like symptoms and also diarrhea complaints lasting for 3-4 days. Considering the current anamnesis and laboratory findings, the patient was thought to have CCHF and the patient was isolated. The serum sample taken from patient with an initial diagnosis of CCHF and sent to Department of Microbiology Reference Laboratory Public Health Agency of Turkey. The patientwas referred to the Antalya Training and Research Hospital. The patient’s CCHF serum result was positive. Ribavirin treatment was not initiated in the patient who was accepted to be in the convalescence period, piperacillin-tazobactam 4 x 4.5 g/day treatment was continued and supportive treatment was given. In the follow-up, as the patient’s neutropenia, thrombocytopenia and lymphocytopenia still continuing, she was transferred to hematology clinic for malignancy examination and bone marrow biopsy performed by hematology and B cell ALL was diagnosed. She was accepted to be convalescent in terms of CCHF and chemotherapy was started for ALL treatment by hematology. The patient is still being followed up by the hematology clinic and allogenic hematopoietic stem cell tranplantation is planned for the patient. As a result, CCHF is a disease that can be confused with many differential diagnosis. With this case, it is aimed to draw attention to the diagnostic difficulties of CCHF and ALL and to be the first case in the literature.