About 10 to 15 percent of the 7,200 (720 to 1080) cases of Hodgkin's disease diagnosed in the United States in 1999 occurred in children ages 16 and younger. The disease is rare in children less than 5 years old. More than 90 percent of children with newly diagnosed Hodgkin's disease are curable.

Hodgkin's develops in the lymph system, which is part of the immune system. The lymphatic system is comprised of vessels that branch out into all parts of the body. The vessels carry lymph, a colorless fluid containing white blood cells called lymphocytes. Groups of bean-shaped organs called lymph nodes are located throughout the body along this network of vessels. Lymph nodes are found in clusters in the abdomen, pelvis, underarms and neck. The spleen, which makes lymphocytes and filters blood; the thymus, an organ under the breastbone; and the tonsils in the throat are also part of the lymph system.

The cervical (in the neck) and mediastinal (in the area between the lungs, breastbone and spine) lymph nodes are the primary sites of Hodgkin's disease. The abdominal lymph nodes and spleen may also be affected, as well as the lymphoid components of the lung, liver and bone marrow. Because Hodgkin's disease tends to compress rather than invade, it usually does not impair the function of various organs.

The disease can spread contiguously, through the lymphatic vessels, or hematogenously, which means involving the bone and marrow (spongy tissue inside bones).