A condition that occurs when donated stem cells or bone marrow (the graft) see the healthy tissues in the patient’s body (the host) as foreign and attack them. It can also occur after an organ transplant. GVHD can cause damage to the host’s tissues and organs, especially the skin, liver, intestines, eyes, mouth, hair, nails, joints, muscles, lungs, kidneys, and genitals. The signs and symptoms may be severe and life threatening. GVHD can occur within the first few months after transplant (acute) or much later (chronic). Also called graft-versus-host disease.