Kaposi's sarcoma. Enlargement of the occipital lymph nodes on the back of the head due to Kaposi's sarcoma, in a patient with AIDS. Enlargement of the nodes is usually more symmetrical than seen here. AIDS (acquired immune deficiency syndrome) is a disease caused by the human immunodeficiency virus (HIV). It causes a gradual weakening of the immune system, making otherwise harmless infections life-threatening. Kaposi's sarcoma is a type of skin cancer. In AIDS it often spreads to other tissues and can be rapidly fatal. This image was taken in Africa, where lack of access to medicine and information makes AIDS a major public health concern.