Hydroxyurea is an antineoplastic agent used alone or in combination with other chemotherapeutic drugs or radiation in the treatment of resistant leukemias and carcinomas of the head and neck. It is also useful to increase fetal hemoglobin concentration, thus reducing the frequency of severe crisis and reducing the necessity for blood transfusions in patients with sickle cell anemia.

They also use hydroxyurea off-label in the treatment of polycythemia vera, essential thrombocythemia, psoriasis, acute myeloid leukemia, meningioma, melanoma, and ovarian cancer.