A procedure in which a small sample of bone marrow (soft, sponge-like tissue in the centre of most bones) and bone is removed. A small area of skin and the surface of the bone underneath are numbed with an anesthetic. Then a special wide needle is pushed into the bone. A sample of liquid bone marrow is removed with a syringe attached to the needle. The syringe is then removed and the needle is rotated to remove a sample of the bone and the bone marrow. Both the bone marrow and bone samples are sent to a laboratory to be looked at under a microscope.