Hematological alterations may be the first sign in the oral cavity and symptoms vary depending on the cell line that is affected: Erythrocytes, leukocytes and platelets. The formation of blood cells are held in the bone marrow through a process called hematopoiesis, which is responsible for training, development and specialization in all its functional blood cells, they move from pluripotent stem cell to hematopoietic cells mature emerging to peripheral blood. The dentist must be able to identify the different signs in the oral cavity that could suggest that the patient has a haematological disorder, which could complicate dental treatment. The timely identification of these signs through a thorough physical examination and the complete clinical history prevents complications from occurring in the patient and may put their lives at risk, so when finding any sign suggestive of a hematological disorder should refer to the patient with the hematologist.