Microcytic anaemia is a medical condition in which the red blood cells are smaller than normal, leading to a decrease in the hemoglobin levels. There are several synonyms for microcytic anemia, including hypochromic microcytic anemia, microcytosis, iron deficiency anemia, and sideropenia. Hypochromic microcytic anemia is a type of anemia characterized by decreased hemoglobin concentration and red blood cells that are smaller and paler than normal. Microcytosis is a condition in which the red blood cells are smaller than usual, but the hemoglobin concentration is normal or elevated. Iron deficiency anemia is the most common type of anemia worldwide and is often accompanied by microcytosis. Sideropenia is a synonym for iron deficiency, reflecting the fact that iron is essential for the production of hemoglobin in the red blood cells.