Hematologists are medical doctors who specialize in the diagnosis and treatment of diseases of the blood and blood system, such as anemia, blood-clotting disorders, and leukemia. Hematologists may also perform procedures such as bone marrow aspiration and biopsy, order blood transfusions, or diagnose blood disorders.

Hematologists may be internists or pathologists who further specialize in disorders of the blood. Hematologists can be board-certified in hematology through the Board of Internal Medicine or the American Board of Pathology, which are recognized by the American Board of Medical Specialties.